MLB Baseball Terminology Reference Table
134 MLB terms across 8 categories, covering hitting, pitching, defense, strategy, rules, roster moves and teams, with modern metrics such as WAR and wRC+.
Data last maintained
MLB Baseball Terminology Reference Table
134 MLB terms across 8 categories, covering hitting, pitching, defense, strategy, rules, roster moves and teams, with modern metrics such as WAR and wRC+.
Data last maintained
Learn the terms by following a match
- 9 fielders per team
- 9 innings, 3 outs per half-inning
- Bases 27.43 m (90 ft) apart
Meet baseball (MLB)
This figure is the whole field seen from above, with home plate at the bottom and the outfield at the top: home plate and first, second and third base form a diamond (the infield), and the big area of grass beyond it is the outfield; the 9 fielders are in place and the batter stands in the batter's box beside home plate.
In baseball the two teams take turns attacking and fielding: the fielding team spreads 9 players around the field, and the attacking team sends up one player at a time to bat. The pitcher throws the ball towards home plate, the batter hits it with the bat and then runs to first base.
Going round the diamond, a runner who touches first, second and third base in order and gets back to home plate scores 1 run. Once the attacking team has 3 “outs”, its half of the inning ends and the teams swap (the fielding side bats).
Each team batting once makes one inning; after 9 innings the team with more runs wins, and a tie is played on (extra innings). The next four pages look, in order, at strikes and balls, how to reach base and score, recent rule changes and the nine fielding positions.
This page follows MLB; where NPB and CPBL differ:
Designated hitterNPB's Central League adopts it only in 2027; MLB and the CPBL already use it.
Pitch clockMLB 15/18 s, CPBL 18/23 s; NPB has not started one yet.
TiesMLB plays until there is a winner; NPB and CPBL regular-season games can end tied after 12 innings.
All Categories
| Term | Abbreviation | Category | Description | Usage & Notes |
|---|---|---|---|---|
Arizona Diamondbacks ARI | ARI | National League West franchise (est. 1998) playing home games at Chase Field in Phoenix, Arizona. | Common nicknames: D-backs and Snakes. Scoreboards list them as ARI. | |
Colorado Rockies COL | COL | National League West franchise (est. 1993) playing home games at Coors Field in Denver, Colorado. | Common nicknames: Rox and Rockies. Scoreboards list them as COL. | |
Los Angeles Dodgers LAD | LAD | National League West franchise (est. 1883) playing home games at Dodger Stadium in Los Angeles, California. | Common nicknames: Dodgers and Boys in Blue. Scoreboards list them as LAD. | |
San Diego Padres SD | SD | National League West franchise (est. 1969) playing home games at Petco Park in San Diego, California. | Common nicknames: Pads and Friars. Scoreboards list them as SD. | |
San Francisco Giants SF | SF | National League West franchise (est. 1883) playing home games at Oracle Park in San Francisco, California. | Common nicknames: Giants and Orange and Black. Scoreboards list them as SF. | |
Atlanta Braves ATL | ATL | National League East franchise (est. 1876) playing home games at Truist Park in Cumberland, Georgia. | Common nicknames: Braves and Bravos. Scoreboards list them as ATL. | |
Miami Marlins MIA | MIA | National League East franchise (est. 1993) playing home games at loanDepot park in Miami, Florida. | Common nicknames: Marlins and Fish. Scoreboards list them as MIA. | |
New York Mets NYM | NYM | National League East franchise (est. 1962) playing home games at Citi Field in Queens, New York. | Common nicknames: Mets and Amazin's. Scoreboards list them as NYM. | |
Philadelphia Phillies PHI | PHI | National League East franchise (est. 1883) playing home games at Citizens Bank Park in Philadelphia, Pennsylvania. | Common nicknames: Phillies and Fightin' Phils. Scoreboards list them as PHI. | |
Washington Nationals WSH | WSH | National League East franchise (est. 1969) playing home games at Nationals Park in Washington, DC. | Common nicknames: Nats and Nationals. Scoreboards list them as WSH. | |
Chicago Cubs CHC | CHC | National League Central franchise (est. 1876) playing home games at Wrigley Field in Chicago, Illinois. | Common nicknames: Cubbies and North Siders. Scoreboards list them as CHC. | |
Cincinnati Reds CIN | CIN | National League Central franchise (est. 1882) playing home games at Great American Ball Park in Cincinnati, Ohio. | Common nicknames: Reds and Big Red Machine. Scoreboards list them as CIN. | |
Milwaukee Brewers MIL | MIL | National League Central franchise (est. 1969) playing home games at American Family Field in Milwaukee, Wisconsin. | Common nicknames: Crew and Brew Crew. Scoreboards list them as MIL. | |
Pittsburgh Pirates PIT | PIT | National League Central franchise (est. 1882) playing home games at PNC Park in Pittsburgh, Pennsylvania. | Common nicknames: Pirates and Bucs. Scoreboards list them as PIT. | |
St. Louis Cardinals STL | STL | National League Central franchise (est. 1882) playing home games at Busch Stadium in St. Louis, Missouri. | Common nicknames: Cards and Redbirds. Scoreboards list them as STL. | |
Baltimore Orioles BAL | BAL | American League East franchise (est. 1954) playing home games at Oriole Park at Camden Yards in Baltimore, Maryland. | Common nicknames: O's and Birdland. Scoreboards list them as BAL. | |
Boston Red Sox BOS | BOS | American League East franchise (est. 1901) playing home games at Fenway Park in Boston, Massachusetts. | Common nicknames: Red Sox and BoSox. Scoreboards list them as BOS. | |
New York Yankees NYY | NYY | American League East franchise (est. 1901) playing home games at Yankee Stadium in Bronx, New York. | Common nicknames: Yankees and Bronx Bombers. Scoreboards list them as NYY. | |
Tampa Bay Rays TB | TB | American League East franchise (est. 1998) playing home games at Tropicana Field in St. Petersburg, Florida. | Common nicknames: Rays and Devil Rays. Scoreboards list them as TB. | |
Toronto Blue Jays TOR | TOR | American League East franchise (est. 1977) playing home games at Rogers Centre in Toronto, Ontario. | Common nicknames: Blue Jays and Jays. Scoreboards list them as TOR. | |
Chicago White Sox CWS | CWS | American League Central franchise (est. 1901) playing home games at Rate Field in Chicago, Illinois. | Common nicknames: White Sox and South Siders. Scoreboards list them as CWS. | |
Cleveland Guardians CLE | CLE | American League Central franchise (est. 1901) playing home games at Progressive Field in Cleveland, Ohio. | Common nicknames: Guardians and Guards. Scoreboards list them as CLE. | |
Detroit Tigers DET | DET | American League Central franchise (est. 1901) playing home games at Comerica Park in Detroit, Michigan. | Common nicknames: Tigers and Motor City Kitties. Scoreboards list them as DET. | |
Kansas City Royals KC | KC | American League Central franchise (est. 1969) playing home games at Kauffman Stadium in Kansas City, Missouri. | Common nicknames: Royals and Boys in Blue. Scoreboards list them as KC. | |
Minnesota Twins MIN | MIN | American League Central franchise (est. 1901) playing home games at Target Field in Minneapolis, Minnesota. | Common nicknames: Twins and Twinkies. Scoreboards list them as MIN. | |
Houston Astros HOU | HOU | American League West franchise (est. 1962) playing home games at Daikin Park in Houston, Texas. | Common nicknames: Astros and Stros. Scoreboards list them as HOU. | |
Los Angeles Angels LAA | LAA | American League West franchise (est. 1961) playing home games at Angel Stadium in Anaheim, California. | Common nicknames: Angels and Halos. Scoreboards list them as LAA. | |
Athletics ATH | ATH | American League West franchise (est. 1901) playing home games at Sutter Health Park in West Sacramento, California. | Common nicknames: A's and Green and Gold. Scoreboards list them as ATH. | |
Seattle Mariners SEA | SEA | American League West franchise (est. 1977) playing home games at T-Mobile Park in Seattle, Washington. | Common nicknames: Mariners and M's. Scoreboards list them as SEA. | |
Texas Rangers TEX | TEX | American League West franchise (est. 1961) playing home games at Globe Life Field in Arlington, Texas. | Common nicknames: Rangers and Lone Star Nine. Scoreboards list them as TEX. | |
Launch Angle | Vertical angle at which the ball leaves the bat relative to the ground. | Optimizing launch angle helps produce line drives and home runs. | ||
Exit Velocity EV | EV | Speed of the baseball as it leaves the bat, typically measured in miles per hour. | Higher exit velocity correlates with stronger contact and better offensive outcomes. | |
Barrel | Statcast classification for batted balls with optimal exit velocity and launch angle combinations. | Barrel rate is a shorthand for how often a hitter produces elite contact. | ||
Hard-Hit Rate | Percentage of batted balls struck at 95 miles per hour or harder. | Highlights hitters who consistently drive the ball with authority. | ||
Bat Speed | The rate at which the bat travels through the hitting zone, often tracked by motion sensors. | Faster bat speed allows hitters to wait longer and still drive the ball with power. | ||
Sweet Spot Percentage | Share of batted balls hit with a launch angle between 8 and 32 degrees, the most productive window. | Complements exit velocity by identifying hitters who live in the best contact window. | ||
Line Drive | Batted ball hit on a relatively low, straight trajectory with minimal arc. | Produces the highest batting average of any batted-ball type. | ||
Fly Ball | Batted ball hit on an upward trajectory that stays in the air for an extended time. | Fly-ball hitters often trade batting average for slugging potential. | ||
Ground Ball | Batted ball that strikes the ground quickly and stays on the infield surface. | Ground-ball-heavy hitters rely on speed and finding holes rather than power. | ||
Pull Hitter | Batter who most often hits the ball to the side of the field corresponding to his pull hand. | Pull hitters face defensive shifts but can generate power by turning on pitches. | ||
Opposite-Field Hitter | Batter who frequently drives the ball to the field opposite his pull side. | Opposite-field approach counters shifts and indicates strong plate coverage. | ||
Spray Chart | Visual plot showing where a hitter's batted balls land across the field. | Coaches study spray charts to design defensive positioning and identify tendencies. | ||
Plate Discipline | A hitter's ability to distinguish strikes from balls and choose which pitches to swing at. | Strong plate discipline leads to more walks, fewer chases, and better counts. | ||
Chase Rate | Percentage of swings at pitches located outside the strike zone. | Lower chase rates signify patience and sharpen on-base skills. | ||
Contact Rate | Percentage of swings that result in the batter making contact with the ball. | High contact rates reduce strikeouts and sustain table-setting hitters. | ||
Situational Hitting | Approach focused on advancing runners or producing the needed result rather than personal stats. | Includes executing sacrifice flies, hitting behind the runner, or shortening the swing with two strikes. | ||
Hit by Pitch HBP | HBP | The batter is struck by a pitch without swinging and is awarded first base, even if the ball only touches the uniform or protective gear. | A strike takes precedence: if the batter swung or the pitch was in the strike zone, it is not a hit-by-pitch. | |
Base Hit H | H | A fair ball that lets the batter reach base safely without the help of an error or a fielder's choice; it is a single, double, triple or home run depending on the bases reached. | Batting average is hits divided by at-bats; the box score lists hits in the H column. | |
Home Run HR | HR | A hit on which the batter rounds all the bases and scores, usually by driving a fair ball over the outfield fence; an inside-the-park home run stays in play. | Every runner on base scores too; a grand slam is a home run with the bases loaded, worth four runs. | |
Four-Seam Fastball | Straightest and firmest fastball gripped across the seams to create backspin and ride. | Primary pitch for many starters and relievers to establish counts and elevate for strikeouts. | ||
Two-Seam Fastball | Fastball gripped along the seams that features arm-side movement and sink. | Generates ground balls and weak contact when located down in the zone. | ||
Sinker | Hard fastball variant with heavy downward movement designed to induce grounders. | Effective when started at the knees and allowed to dive below barrels. | ||
Cutter | Fastball with late glove-side movement that breaks bats and misses barrels. | Mariano Rivera popularized the pitch as a late-inning weapon against both handednesses. | ||
Slider | Breaking ball thrown with tight spin that sweeps laterally with some depth. | Used as a chase pitch when buried or as a backdoor strike when started off the plate. | ||
Curveball | Arcing breaking ball with significant top-spin that causes sharp downward break. | Effective when tunneled off fastballs to disrupt timing and eye level. | ||
Changeup | Off-speed pitch thrown with fastball arm action to disrupt timing with reduced velocity. | Most effective fading away from opposite-handed hitters to induce weak contact. | ||
Splitter | Pitch gripped between the index and middle fingers that drops sharply late. | Works as a strikeout pitch when tunneled off the fastball due to late tumble. | ||
Knuckleball | Slow pitch thrown with minimal spin that dances unpredictably through the air. | Requires a specialized catcher and can neutralize power lineups when commanded. | ||
Spin Rate RPM | RPM | Revolutions per minute generated on a pitch, influencing movement and perceived rise or drop. | Higher spin boosts hop on fastballs and sharpens breaking pitches when paired with proper axis. | |
Pitch Tunneling | Designing pitch sequences so multiple offerings share the same early trajectory before diverging late. | Enhances deception, making fastballs and breaking balls harder to distinguish for hitters. | ||
Pitch Count | Total number of pitches thrown by a pitcher in an outing or over a season. | Teams monitor pitch counts to manage fatigue, injury risk, and bullpen planning. | ||
Walks plus Hits per Inning Pitched WHIP | WHIP | Measures how many baserunners a pitcher allows per inning via walks and hits. | Lower WHIP indicates better command and fewer baserunners against the pitcher. | |
Opener Strategy | Deploying a reliever to start the game for one or two innings before handing the ball to a bulk pitcher. | Helps teams manage matchups at the top of the order and protect young starters. | ||
Strikeout K | K | An out recorded when the pitcher throws three strikes to a batter, swinging or looking; a foul cannot be the third strike, but a foul tip caught by the catcher is. | Scorers write K for a swinging strikeout and a backwards K for a called third strike; if the catcher drops strike three, the batter may run to first when it is open or there are two outs. | |
Walk BB | BB | The batter is awarded first base after the pitcher throws four pitches outside the strike zone that the batter does not swing at. | Runners advance only if forced; a walk with the bases loaded scores a run and credits the batter with an RBI. | |
Infield Shift | Positioning infielders around a hitter tendency while staying within current MLB limits on infield alignment. | Since 2023, four infielders must stay on the infield and cannot switch sides; four-outfielder alignments are prohibited. | ||
Double-Play Depth | Infielders position themselves slightly closer to second base to turn double plays more quickly. | Common when there's a runner on first with fewer than two outs and a ground-ball pitcher on the mound. | ||
Infield In | Moving all infielders closer to home plate to cut down a runner trying to score. | Used with a runner on third and fewer than two outs in late-inning, one-run situations. | ||
Corners In | First and third basemen charge closer to home plate to defend against a bunt or squeeze play. | Triggered when the batter is a good bunter or the situation suggests a squeeze attempt. | ||
No-Doubles Defense | Outfielders play deeper and corner infielders guard the lines to prevent extra-base hits. | Common in late innings when protecting a narrow lead and the tying run is on base. | ||
Wheel Play | Third baseman charges the bunt while shortstop covers third and first baseman crashes with second covering first. | Used to defend against squeeze bunts with a runner on third and one out or fewer. | ||
Cutoff Man | Infielder who positions himself between the outfielder and the target base to redirect a throw. | Keeps throws on line and allows defenses to adjust the target once the play develops. | ||
Relay Throw | A two-step throw from the outfield to an infielder and onward to a base to retire a runner. | Critical on deep hits when the outfielder cannot reach the target base with one throw. | ||
Tag Play | Defensive action of touching a runner with the ball or glove while holding the ball to record an out. | Essential on steals, rundowns, and plays at the plate where force plays do not apply. | ||
Rundown | Fielders trap a runner between bases, exchanging throws until he is tagged out or escapes. | Requires short, controlled throws and decisive tags to avoid errors that allow advancement. | ||
Outfield Assist | When an outfielder throws to a base or home plate to retire an advancing runner. | Highlights strong outfield arms and accurate throws that change innings. | ||
Pitch Framing | Catcher's subtle glove movements that present borderline pitches as strikes to the umpire. | Analytics now quantify framing value, influencing catcher evaluations and playing time. | ||
Error E | E | Charged by the official scorer when a fielder fails to make a play an average fielder should have made, letting a batter reach or a runner advance. | Notation uses position numbers, so E6 is an error by the shortstop; runs that score because of errors do not count as RBIs and may be unearned for the pitcher. | |
Double Play DP | DP | Two offensive players put out in the same continuous play, most often a ground ball thrown to second and then to first. | Scorers write the route as position numbers, as in 6-4-3 (shortstop to second baseman to first baseman); defenses play double-play depth to set it up. | |
Force Out | An out made by touching the base a runner is forced to advance to, because the batter became a runner, before the runner gets there; no tag is needed. | If the trailing runner or the batter is put out first, the force is removed and the lead runner must be tagged instead. | ||
Small Ball | Offensive approach focused on bunting, stealing, and advancing runners one base at a time. | Used when teams value a single run, often in tight games or pitcher duels. | ||
Hit and Run | The runner breaks for the next base as the batter swings to put the ball in play behind them. | Designed to stay out of double plays and open gaps by moving infielders. | ||
Squeeze Play | Runner on third breaks for home as the batter bunts, aiming to score before the defense can field the ball. | High-risk move often reserved for late innings when a single run is vital. | ||
Safety Squeeze | Variation of the squeeze where the runner waits to break from third until the batter deadens the bunt. | Employed when managers want insurance the ball is down before sending the runner. | ||
Sacrifice Bunt | Batter bunts the ball intending to be thrown out while advancing a baserunner into scoring position. | Most common with a light-hitting pitcher or late in tie games to play for a single run. | ||
Double Switch | National League tactic where a manager substitutes a pitcher and position player simultaneously to reorder the batting lineup. | Keeps a reliever out of the imminent batter's box and maximizes matchup flexibility late in games. | ||
Bullpen Day | Game planned around multiple relievers covering all innings instead of a traditional starter. | Used to manage workloads during congested schedules or when a rotation spot lacks a healthy starter. | ||
Platoon Advantage | Strategy of aligning hitters and pitchers to exploit favorable left-right matchups. | Managers rotate platoon partners to keep hitters fresh and press the advantage late in games. | ||
Intentional Walk Strategy | Choosing to award first base to a hitter to create a force play, set up a double play, or face a weaker matchup. | Managers weigh game state, base occupancy, and the on-deck hitter before issuing the four-finger signal. | ||
Stolen Base SB | SB | A runner advancing to a base he is not entitled to, usually while the pitcher delivers, but also during a pickoff attempt or the catcher's return throw. | A failed attempt is scored as caught stealing (CS); since 2023 larger bases and limits on pickoff throws have made steals more common. | |
Batting Average AVG | AVG | Ratio of a hitter's hits to official at-bats. | Long-time standard for measuring contact ability, though it ignores walks and power. | |
On-Base Percentage OBP | OBP | Measures how often a batter reaches base via hit, walk, or hit-by-pitch per plate appearance. | Rewards players who work counts and reach base beyond pure hitting average. | |
Slugging Percentage SLG | SLG | Total bases divided by at-bats, weighting extra-base hits more heavily than singles. | Combined with OBP to gauge overall offensive production. | |
On-base Plus Slugging OPS | OPS | Sum of on-base percentage and slugging percentage as a quick measure of overall offense. | Useful shorthand for comparing hitters across eras, though it values all components equally. | |
OPS Plus OPS+ | OPS+ | Normalizes OPS for league and park factors, centering 100 as league average. | Values above 100 indicate above-average production while below 100 signals below-average hitters. | |
Weighted On-base Average wOBA | wOBA | Assigns run-value weights to different outcomes to better capture offensive contribution per plate appearance. | Core component of advanced metrics like wRC+ and more predictive than OPS alone. | |
Weighted Runs Created Plus wRC+ | wRC+ | Adjusts weighted runs created for league and park, scaling 100 as average offensive output. | Preferred stat for comparing hitters across environments because it weights events and context. | |
Wins Above Replacement WAR | WAR | Comprehensive metric estimating how many wins a player adds compared to a replacement-level player. | Used to compare overall value across positions; different providers publish slightly different WAR formulas. | |
Batting Average on Balls in Play BABIP | BABIP | Batting average calculated only on balls hit into the field of play, excluding home runs and strikeouts. | Highlights luck and defense behind outcomes; extreme BABIP swings often regress toward career norms. | |
Earned Run Average ERA | ERA | Average number of earned runs a pitcher allows per nine innings pitched. | Traditional pitching barometer, though influenced by defense and scoring decisions. | |
Fielding Independent Pitching FIP | FIP | Estimates pitcher performance based on strikeouts, walks, hit batters, and home runs, removing defensive impact. | Better predictor of future ERA than past ERA because it focuses on outcomes pitchers control. | |
Strikeout Rate K% | K% | Percentage of batters faced that a pitcher strikes out, or of plate appearances a hitter ends in strikeouts. | High strikeout rates limit balls in play and are prized for both pitchers and hitters' evaluation. | |
Walk Rate BB% | BB% | Percentage of plate appearances that result in a walk, for either pitchers or hitters. | Low walk rates signal pitcher control, while high rates reflect hitter patience. | |
Strikeout-to-Walk Ratio K/BB | K/BB | Ratio comparing strikeouts to walks, illustrating command and dominance. | Higher ratios mean pitchers avoid free passes while missing bats at elite rates. | |
Quality Start QS | QS | Start in which a pitcher works at least six innings and allows three earned runs or fewer. | Serves as a baseline for dependable outings, though it does not account for bullpen leverage or dominance. | |
Left on Base Percentage LOB% | LOB% | Share of baserunners a pitcher strands on base without allowing them to score. | Extreme strand rates tend to regress and help evaluate whether ERA aligns with peripherals. | |
Save SV | SV | Credited to a relief pitcher who finishes a game for the winning team under specific leverage conditions. | Traditional measure for closers, though modern analysis also weighs leverage index and strikeout skills. | |
Run Batted In RBI | RBI | Credited to a batter when his plate appearance results in a run scoring, except when the run scores on an error or while he grounds into a double play. | Run-scoring hits, bases-loaded walks or hit-by-pitches and run-scoring outs such as a sacrifice fly all count; a solo home run is one RBI. | |
Infield Fly Rule | Declares the batter out on a fair infield pop-up with runners on base and fewer than two outs to prevent easy double plays. | Umpires call "Infield Fly, batter's out" while the ball is in the air; runners may advance at their own risk. | ||
Pitch Clock | Uses a 30-second timer between batters plus a pitch timer of 15 seconds with bases empty and 18 seconds with runners on base. | Pitcher violations add an automatic ball; batter violations add an automatic strike when they are not ready by the required mark. | ||
Balk | Illegal pitching movement with runners on base that deceives the runner, resulting in all runners advancing one base. | Common balk calls include failing to come set, flinching during the stretch, or faking a throw to first without stepping off. | ||
Designated Hitter Rule DH | DH | Allows teams to bat a designated hitter in place of the pitcher without forfeiting the pitcher's defensive role. | Adopted universally in 2022, the DH boosts offense and extends careers for limited-fielding sluggers. | |
Three-Batter Minimum | Requires relief pitchers to face at least three batters or finish an inning before being replaced, barring injury. | Introduced to curb excessive matchup pitching changes and speed up late innings. | ||
Challenge System | Allows managers a limited number of video review challenges to overturn umpire calls on the field. | Each club starts with one challenge per game and retains it if the call is overturned. | ||
Obstruction | When a fielder without the ball impedes a runner's progress, the runner is awarded the base they would have reached. | Often occurs on rundowns or when catchers block the plate without possession under updated safety rules. | ||
Batter Interference | When the batter hinders the catcher or fielder during a play, resulting in the batter being called out and runners returning. | Includes stepping outside the batter's box on a steal attempt or contacting the catcher on a throw. | ||
Force-Play Slide Rule | Requires runners to make a bona fide slide on force plays to protect fielders and avoid malicious takeout attempts. | Established after the 2016 Chase Utley incident, violations result in both runner and batter-runner being called out. | ||
Extra-Innings Runner | Regular-season rule placing the player immediately before the half-inning's leadoff hitter on second base to start each extra half-inning. | It applies only in regular-season games; postseason extra innings are played without an automatic runner. | ||
Inning | One of the nine periods of a regulation game; each team bats once, the visitors in the top half and the home team in the bottom half, and each half ends after three outs. | If the home team leads after the top of the 9th, the bottom half is not played; a tie after nine goes to extra innings. | ||
Out | A batter or runner being retired, most often by a strikeout, a caught fly ball, a force out or a tag; three outs end the half-inning. | Broadcasts pair the outs with the bases, as in "one out, runner on second"; strategy such as bunting or tagging up depends on how many outs there are. | ||
Strike Zone | The area over home plate from the midpoint between the batter's shoulders and the top of the uniform pants down to a point just below the kneecap, judged in the batting stance. | A pitch that passes through any part of the zone without a swing is a called strike; the plate umpire judges it, subject to the challenge system. | ||
Count | The number of balls and strikes on the current batter; four balls is a walk and three strikes is a strikeout. | English broadcasts say balls first, so "3-2" is a full count; hitters' counts such as 2-0 favour the batter. | ||
Foul Ball | A batted ball that settles or is first touched in foul territory, outside the foul lines; it counts as a strike until the batter has two strikes. | With two strikes a foul does not end the at-bat, except a foul bunt or a foul tip caught by the catcher; a foul caught in the air is an out. | ||
Active Roster | Group of 26 players eligible to play in a major league game during the regular season. | Clubs shuffle the active roster daily to balance bullpen coverage, bench bats, and matchups. | ||
40-Man Roster | Club's protected list of players eligible for the major league, including those optioned to the minors. | Teams must add prospects to the 40-man roster to shield them from the Rule 5 Draft. | ||
Option Year | Season in which a 40-man player can be moved between the majors and minors without clearing waivers. | A player typically has three option years; exhausting them requires clearing waivers before another demotion. | ||
Injured List IL | IL | Roster designation removing an injured player from the active roster for 10, 15, or 60 days. | Players on the 60-day IL free a 40-man spot, while shorter stints keep the club from playing short-handed. | |
Designated for Assignment DFA | DFA | Transaction giving a team seven days to trade, waive, or release a player while freeing a roster spot. | Common when a team needs to add a new acquisition or activate a player returning from the injured list. | |
Service Time | Accumulated days a player spends on the major league roster or injured list, impacting pay and free agency. | Teams sometimes option players late in the season to manage service time milestones and arbitration clocks. | ||
Arbitration Eligibility | Status allowing players with three-plus years of service (or Super Two) to have salaries decided by arbitration. | Clubs and players exchange salary figures before a hearing if they cannot agree on a contract. | ||
Super Two | Designation for players with at least two years of service and in the top 22% of time among that class, granting early arbitration. | Super Two status often delays promotions as teams attempt to avoid adding an extra year of arbitration. | ||
Non-Roster Invitee NRI | NRI | Player not on the 40-man roster who is invited to major league spring training camp. | NRIs can win roster spots with strong camps or serve as depth options kept in Triple-A. | |
Waiver Claim | Process by which a team acquires a player placed on waivers by another club, assuming his contract. | Claim priority is determined by reverse standings early in the season and by league record after July 1. | ||
Taxi Squad | Group of extra players traveling with the team who can be activated quickly in case of injury or illness. | Became prominent during travel restrictions and remains useful for doubleheaders or emergency coverage. |
About MLB Baseball Terminology Reference Table
Stats, roster rules, teams, and game language
The table covers hitting, pitching, defensive alignments, strategy, advanced stats, rules, roster management, and team nicknames. It is intended for reading box scores, broadcasts, and transaction news, not for live scoring or player projection.
Move between sabermetrics and rules
Search can match localized terms, English labels, abbreviations, aliases, and keywords. Category filters keep stats, roster rules, team names, and on-field concepts separate so you can isolate WAR-style metrics, option rules, or defensive terms quickly.
Not a transaction desk or fantasy engine
MLB rules, park names, standings, roster mechanisms, and stat formulas can change by season or data provider. Confirm current MLB, club, league, scoring, and fantasy-platform sources before using a term for contracts, roster moves, betting, or official analysis.
FAQ
Common questions and answers about this topic.
Which baseball terms should a beginner learn first?
Start with hitting and pitching basics, then use the category filters for defense, strategy, stats, rules, roster moves, and teams. You can search an abbreviation such as AVG or ERA, an English broadcast term, or a translated term to jump to its explanation.
How do I read AVG, OBP, SLG, OPS, and ERA in a box score?
Batting Average (AVG) is hits per official at-bat. On-Base Percentage (OBP) also counts reaching base by a hit, walk, or hit-by-pitch. Slugging Percentage (SLG) weights total bases, and On-base Plus Slugging (OPS) adds OBP and SLG. For pitchers, Earned Run Average (ERA) is earned runs allowed per 9 innings.
What is the difference between OPS and OPS+?
On-base Plus Slugging (OPS) simply adds OBP and SLG for a quick offensive measure. OPS Plus (OPS+) adjusts that result for league and ballpark context, with 100 set as league average; above 100 is above average and below 100 is below average.
How are WAR and wRC+ different?
Weighted Runs Created Plus (wRC+) measures offensive production after adjusting for league and ballpark, with 100 as average. Wins Above Replacement (WAR) estimates a player's total value in wins versus a replacement-level player and can compare positions, but its formula varies by provider.
What do the 26-man roster, 40-man roster, options, and waivers mean?
The Active Roster is the 26 players eligible for a regular-season major league game. The 40-Man Roster is the club's protected pool, including players optioned to the minors. During an Option Year, a player on that 40-player list can move between the majors and minors without clearing waivers; players typically have 3 option years. A Waiver Claim lets another club acquire a waived player and assume the contract.
Can I search by an abbreviation or a term heard on a broadcast?
Yes. Search matches abbreviations, English labels, translated terms, aliases, and related keywords. If a result is too broad, choose a category such as hitting, pitching, stats, rules, or roster management to narrow the table.
Data Sources
This tool's data is compiled from the authoritative sources below.
- MLB team location information(opens in a new tab)
- MLB 2026 standings(opens in a new tab)
- MLB glossary - Pitch Timer(opens in a new tab)
- MLB glossary - Designated Runner(opens in a new tab)
- MLB glossary - Defensive Shift Limits(opens in a new tab)
- MLB glossary - Strike Zone(opens in a new tab)
- MLB glossary - Standard Stats(opens in a new tab)
- MLB announces 2026 Postseason schedule(opens in a new tab)
- MLB releases 2027 regular-season schedule(opens in a new tab)
Data last maintained