Baseball Glossary
Key terms and concepts, explained in plain English.
Balk
A balk is an illegal motion by the pitcher with runners on base, such as a deceptive or interrupted delivery, intended to prevent deceiving base runners. The penalty is that all runners advance one base.
Batting Average (AVG)
Batting average is the ratio of a batter's hits to official at-bats, expressed as a three-digit decimal such as .300. It excludes walks, hit-by-pitches, and sacrifices, measuring how often a hitter reaches base via a hit.
Bullpen
The bullpen is both the area where relief pitchers warm up during a game and the collective group of a team's relief pitchers. Managers rely on the bullpen to replace the starter and protect leads late in games.
Bunt
A bunt is a batted ball produced by holding the bat still or loosely to tap the ball softly into the infield rather than taking a full swing. It is used to advance runners, beat out an infield hit, or catch the defense off guard.
Count
The count is the current tally of balls and strikes on the batter during a plate appearance, always stated with balls first, such as two-and-one. It shapes strategy for both the pitcher and the hitter.
Designated Hitter (DH)
The designated hitter is a player who bats in place of the pitcher without playing a defensive position. The role allows a stronger offensive player to hit while the pitcher focuses solely on pitching, where the rules permit it.
Double Play
A double play is a single continuous defensive sequence that records two outs, most commonly a ground ball turned from second base to first. It is one of the most valuable defensive plays for ending a threat.
Earned Run Average (ERA)
Earned run average is the average number of earned runs a pitcher allows per nine innings, calculated as earned runs times nine divided by innings pitched. Runs scoring due to fielding errors are excluded as unearned.
Error
An error is a fielding mistake, such as a misplayed ground ball or wild throw, that allows a batter or runner to advance when an out or lesser advance should have resulted. Errors are not charged as hits and can produce unearned runs.
Fielder's Choice
A fielder's choice occurs when a fielder handling a batted ball chooses to retire a different base runner instead of the batter, allowing the batter to reach base. The batter is not credited with a hit on the play.
Force Out
A force out occurs when a runner is compelled to advance because the batter became a runner, and a fielder touches the next base while holding the ball before the runner arrives. No tag is required because the runner has no right to the base being approached.
Full Count
A full count is a count of three balls and two strikes, meaning the next ball results in a walk and the next called or swinging strike ends the at-bat. Foul balls prolong the at-bat without changing the count.
Grand Slam
A grand slam is a home run hit with runners on all three bases, driving in four runs on a single swing. It is the most productive single play available to a hitter.
Infield Fly
The infield fly rule declares a batter automatically out on an easily catchable pop-up in fair territory when first and second, or the bases, are occupied with fewer than two outs. It prevents the defense from intentionally dropping the ball to turn a cheap double play.
Inning
An inning is a division of a game in which each team takes a turn batting and a turn fielding, with each half ending after three outs. A regulation game typically consists of nine innings.
Lineup
The lineup is the ordered list of batters a team submits before a game, setting the sequence in which players come to bat. Once established, the batting order must be followed, though substitutions are permitted within a player's slot.
No-hitter
A no-hitter is a complete game in which a pitcher, or combination of pitchers, allows the opposing team no hits. Base runners may still reach via walks, errors, or hit-by-pitches without breaking up the no-hitter.
On-base Percentage (OBP)
On-base percentage measures how frequently a batter reaches base by any means that count toward the total, including hits, walks, and hit-by-pitches. It is calculated as times on base divided by plate appearances, excluding sacrifice bunts.
On-base Plus Slugging (OPS)
OPS is the sum of a player's on-base percentage and slugging percentage, combining the ability to reach base with the ability to hit for power. It is a quick, widely used gauge of overall offensive value.
Run Batted In (RBI)
A run batted in is credited to a batter whose plate appearance drives a runner home, such as with a hit, sacrifice, or bases-loaded walk. Certain plays, like a run scoring on a double-play ground ball, do not earn an RBI.
Sacrifice
A sacrifice is a play in which the batter deliberately makes an out to advance a runner, either by bunting or hitting a deep fly ball that scores a runner. Sacrifices do not count as at-bats and do not lower a batter's average.
Save
A save is credited to a relief pitcher who finishes a game won by his team while meeting specific conditions, typically protecting a lead of three runs or fewer. The pitcher must not be the winning pitcher and must record at least the final out with the tying run relevant.
Slugging Percentage (SLG)
Slugging percentage measures a hitter's power by dividing total bases by at-bats, giving more weight to extra-base hits. A single counts as one base, a double two, a triple three, and a home run four.
Stolen Base
A stolen base is credited when a base runner advances to the next base on his own initiative, usually during a pitch, without the aid of a hit, walk, or error. Success depends on the runner's jump, speed, and the battery's reaction.
Strike Zone
The strike zone is the three-dimensional area over home plate through which a pitch must pass to be called a strike, spanning the plate's width. Its vertical limits run from the midpoint of the batter's torso down to the hollow beneath the kneecap, as the batter stands ready to swing.
Strikeout
A strikeout is recorded when a batter accumulates three strikes during a plate appearance, resulting in an out. Strikes come from swinging misses, called strikes in the zone, or foul balls with fewer than two strikes.
Tag Up
Tagging up is the requirement that a base runner touch his base at the moment a fly ball is caught before legally advancing to the next base. It allows runners to score or advance on deep fly outs, known as sacrifice flies when a run results.
Walk (Base on Balls)
A walk occurs when a batter receives four pitches outside the strike zone that are not swung at, allowing the batter to advance to first base. It is also called a base on balls and does not count as an at-bat.
Walks and Hits per Inning Pitched (WHIP)
WHIP measures how many base runners a pitcher allows per inning by dividing the sum of walks and hits by innings pitched. A lower WHIP indicates a pitcher who limits traffic on the bases.
Wild Pitch
A wild pitch is a pitch so errant that the catcher cannot reasonably control it, allowing one or more runners to advance. It is charged to the pitcher rather than the catcher.