Inning
A segment of the game in which each team gets a turn to bat. An MLB game is normally nine innings.
1ST · The basics
Start here: the words
Read this first. These are the words the rest of the page assumes you know.
The ballpark, to scale
MLB RULE 2.01 · TAP THE LAYERSCore vocabulary22 words used everywhere below
Out
One of the three retirements the defense needs to end the batting team’s half-inning.
Plate appearance
One complete turn at the plate, ending when the batter reaches base, makes an out, or another result ends the turn.
At-bat
A statistical type of plate appearance. Some plate appearances, such as walks, do not count as official at-bats.
Count
The number of balls and strikes on the current batter, written balls first: 3-1 means three balls and one strike.
Strike zone
The area over home plate where a pitch can be called a strike when it meets the rulebook height limits.
Ball
A pitch outside the strike zone that the batter does not swing at.
Strike
A pitch in the strike zone, a swing and miss, or most foul balls before two strikes.
Force play
A situation where a runner must advance because the batter became a runner and is pushing the runners ahead.
Tag play
A runner is out when a fielder holding the ball touches the runner before the runner reaches a safe base, when no force applies.
Fair ball
A batted ball that is in fair territory under the rules and remains live unless another rule stops play.
Foul ball
A batted ball that ends up in foul territory under the rules. Most foul balls count as a strike unless the batter already has two strikes.
Pitch
The ball thrown by the pitcher toward home plate.
Pitch type
A category of pitch such as fastball, slider, curveball, or changeup, each using different speed and movement.
Bullpen
The group of relief pitchers who enter after the starting pitcher or in specialized late-game roles.
Starter
The pitcher who begins the game for a team.
Reliever
A pitcher who enters after the starter.
Cutoff / relay
A fielder used as an intermediate target so an outfielder can move the ball efficiently toward a base or home plate.
Tag up
After a caught fly ball, a runner must retouch the starting base before trying to advance.
Steal
A runner tries to advance during the pitch without waiting for the batter to hit the ball.
Platoon advantage
Using a hitter or pitcher matchup based partly on handedness, because left/right matchups can affect performance.
Run
A point scored when a runner legally touches first, second, third, and home plate in order.
1ST · The basics
The game at a glance
Nine innings; each has a top (the visitors bat) and a bottom (the home team bats). Three outs end a half-inning. There is no clock on the game itself, but since 2023 there is one on the pitcher.
The strike zone and the 2026 ABS challenge
SET THE BATTER’S HEIGHT · TAP TO PITCHInning
Each team gets a turn to bat. The visiting team bats in the top half; home team in the bottom half.
Out
One of three retirements that end a half-inning.
Run
A score, completed when a runner legally touches first, second, third, and home.
At-bat
A plate appearance that ends in most standard batting results; walks and some other events are plate appearances but not at-bats for statistics.
Ball
Pitch outside the strike zone that the batter does not swing at. Four balls award first base.
Strike
Pitch in the zone not swung at, a swing-and-miss, or certain fouls. Three strikes retire the batter.
Foul ball
Batted ball outside fair territory under the rules. With fewer than two strikes, most fouls add a strike; ordinary foul balls do not create strike three.
Hit
Batter reaches safely on fair batted ball without an error/fielder’s choice being the reason.
Walk (BB)
Four balls award first base.
Hit by pitch (HBP)
Batter is struck by a pitch under applicable rules and is generally awarded first base.
Home run
Fair batted ball leaves the park in play or otherwise qualifies, allowing batter and runners to score.
Extra innings
Played when the game remains tied after regulation.
How the game runsRules that shape every inning
- A standard MLB game is scheduled for nine innings.
- Three outs end each half-inning.
- The batting order cycles continuously from one inning to the next.
- Pitch timer (since 2023): 15 seconds with the bases empty, 18 with runners on. The batter must be set and alert with 8 seconds left. A pitcher violation is an automatic ball; a batter violation an automatic strike.
- Disengagements: a pitcher may step off or throw over only twice per plate appearance with runners on. A third, unsuccessful pickoff is a balk: every runner moves up a base.
- Extra innings: each half-inning after the ninth starts with a runner on second base.
- Designated hitter: both leagues have used the DH since 2022, so pitchers rarely bat in MLB.
1ST · The basics
Field and defensive positions
Every fielder has a number used in scorekeeping. A “6-4-3 double play” means shortstop to second baseman to first baseman.
The nine positions
SCOREKEEPING NUMBERS · TAP A FIELDERPitcher (1)
Delivers pitches, fields the center of the diamond, controls running game, and executes pickoffs.
Catcher (2)
Receives pitches, blocks balls, controls running game, communicates signs/strategy, and directs much of the defense.
First baseman (3)
Handles many throws, holds runners, and fields right side.
Second baseman (4)
Middle infielder with range; turns double plays and covers bases.
Third baseman (5)
Handles hard-hit balls and bunts near third; long throw across diamond.
Shortstop (6)
Premium range/arm position; covers left side and anchors many double plays.
Left fielder (7)
Outfielder responsible for left field; backs up throws and reads caroms.
Center fielder (8)
Usually widest outfield range; often takes priority on fly balls.
Right fielder (9)
Outfielder in right; often requires strong arm for throws to third/home.
Designated hitter (DH)
Bats in lineup without playing a defensive position under DH rules.
Cutoff man
Fielder positioned to relay throws from outfield to an appropriate base.
Backing up
Moving behind a teammate/base to stop an overthrow from becoming extra bases.
4TH · Pitcher vs. hitter
The count and plate-appearance strategy
The count (balls first, then strikes) is the single best summary of who is winning the at-bat. Hitters hunt in their counts; pitchers expand the zone in theirs.
All twelve counts
WHO HAS THE ADVANTAGE?0-0
Neutral count. Pitcher wants strike one; hitter decides whether to hunt a specific pitch.
0-1 / 0-2
Pitcher ahead. Hitter protects more of the zone and must respect chase pitches.
1-0 / 2-0 / 3-1
Hitter-favorable counts. Fastball or strike-zone predictability may rise, and hitter can hunt a location.
2-1
Balanced but hitter-friendly. Both sides can still access broad arsenals.
2-2
Battle count. Pitcher can expand; hitter must cover zone without chasing everything.
3-2 full count
Next qualifying pitch decides walk or strikeout unless fouled off. Runners may move on the pitch in some situations.
Protecting the plate
With two strikes, hitter becomes more defensive and prioritizes contact on borderline strikes.
Working the count
Taking/selecting pitches to gain information, reach hitter-favorable counts, or raise pitch count.
Ambush hitting
Attacking an early pitch because it matches a pre-planned zone/pitch expectation.
Two-strike approach
Shortening swing / expanding coverage / prioritizing contact, depending on hitter philosophy.
4TH · Pitcher vs. hitter
Pitch types and what they do
Pitches differ in speed, spin and movement. Movement is measured against a spinless ball: a four-seamer “rises” only compared with how far it would have dropped.
The pitch-movement map
PITCHER’S VIEW · TYPICAL MLB VALUESFour-seam fastball
Usually highest-velocity fastball, often with “ride” or less vertical drop than expected.
Two-seam fastball
Fastball with more arm-side movement/sink depending on pitcher.
Sinker
Fastball variant emphasizing downward and arm-side movement to generate ground balls.
Cutter
Fastball-like pitch with late glove-side movement, smaller than a slider.
Slider
Breaking ball with glove-side and downward movement; speed/movement vary widely.
Sweeper
Slider family with pronounced horizontal glove-side movement.
Curveball
Breaking ball with larger downward component and generally more speed separation than a slider.
Knuckle curve
Curve family thrown with a knuckle/finger-grip variation; not the same as a knuckleball.
Changeup
Thrown with fastball arm action but lower velocity; relies on timing disruption and often arm-side fade.
Circle change
Common changeup grip/type often featuring arm-side movement.
Splitter
Fastball-like release that drops sharply late due to spin/velocity characteristics.
Forkball
Splitter relative with deeper split grip and often more drop/lower velocity.
Knuckleball
Very low-spin pitch with unpredictable movement; rare in modern MLB.
Eephus
Very slow, high-arcing surprise pitch.
The art of itSequencing and tunneling
- Pitching is sequencing: speed, location, movement, eye level, and tunneling matter together.
- A great slider is more effective when the hitter must also respect a fastball from a similar release window.
- Pitchers use “waste” pitches or chase pitches outside the zone when ahead, but falling behind creates walk risk.
4TH · Pitcher vs. hitter
Hitting concepts
Modern hitting is measured at contact: how hard (exit velocity) and at what angle (launch angle). Hard contact in the right window becomes a barrel.
Exit velocity × launch angle
DRAG THE SLIDERSContact
Putting the ball in play. Contact quality matters: weak contact can still produce outs.
Exit velocity
Speed of the batted ball immediately after contact.
Launch angle
Vertical angle of the batted ball.
Barrel
Statcast quality-of-contact classification combining exit velocity and launch angle.
Pull
Hit toward batter’s pull side.
Opposite field
Hit to the field opposite batter’s natural pull side.
Gap power
Ability to drive balls into spaces between outfielders for doubles/triples.
Plate discipline
Swinging at hittable pitches and taking pitches outside the zone.
Chase rate
How often a hitter swings at pitches outside the strike zone.
Zone rate
Share of pitches thrown in the strike zone.
Sacrifice fly
Fly ball that results in a runner scoring after a catch and meets scoring criteria.
Bunt
Intentional deadened contact used for placement, sacrifice, surprise, or squeeze situations.
Hit-and-run
Runner goes on pitch while batter is expected to swing/contact, opening defensive holes and protecting runner.
Run-and-hit
Runner goes, but hitter retains more discretion whether to swing.
7TH · Defense & baserunning
Baserunning
Runners advance on hits, walks, steals and outs. Whether a runner is forced to run decides how the defense can get him out.
Force or tag?
PUT RUNNERS ON · CHOOSE THE OUTSLead
Distance a runner takes off a base before the pitch.
Secondary lead
Additional movement as pitch reaches plate to improve reaction/start.
Stolen base
Runner advances during pitch without benefit of hit/error under scoring rules.
Caught stealing
Runner is put out attempting to steal.
Pickoff
Pitcher/catcher throws to a base to retire or shorten a runner’s lead.
Tag up
Runner retouches original base after a caught fly ball before attempting to advance.
Force play
Runner must advance because batter becomes runner and occupies the base behind.
Tag play
Fielder must physically tag runner (or meet specific base/appeal conditions) because no force exists.
Rundown
Defense traps runner between bases and exchanges throws to apply a tag.
First-to-third
Runner on first tries to reach third on a single, depending on ball location, speed, and arm strength.
Scoring from second
Runner reads ball/outs and attempts to score on a single.
Infield in
Fielders move closer to plate to improve chance of throwing out runner at home; increases risk of grounders getting through.
7TH · Defense & baserunning
Team defense, alignments and relays
Fielders reposition on almost every pitch, for the hitter, the count, the runners and the score. Since 2023 there are limits on how the infield can shift.
Defensive alignments
STANDARD · DP DEPTH · INFIELD IN · NO-DOUBLESThe cutoff and relay, animated
SINGLE TO RIGHT · RUNNER FROM FIRSTDouble-play depth
Middle infielders position to turn two quickly.
Corners in
First/third baseman move closer for bunt defense or runner-at-third situations.
No-doubles defense
Outfielders play deeper to prevent extra-base hits late with a lead.
Outfield shift
Outfielders move based on hitter spray tendencies, pitch plan, and game situation.
Infield positioning restrictions
Since 2023: when the pitch is released, all four infielders must have both feet on the infield dirt, with two on each side of second base. Infielders cannot switch sides unless there is a substitution.
Cutoff
Relay throw is directed through a cutoff fielder to control runners and improve accuracy.
Relay
Long throw chain from outfield toward a distant base/home.
Priority
Center fielder generally has priority on many outfield fly balls; communication prevents collisions.
Backup responsibility
Non-primary fielders move behind likely throw destination to contain errors.
Bunt defense
Corners charge; middle infield/pitcher/catcher rotate to cover bases depending on runners.
First-and-third defense
Special plays designed to control a stealing runner while preventing runner on third from scoring.
Wheel play
Aggressive bunt defense with corner infielders charging and middle infielders rotating.
7TH · Defense & baserunning
Pitching strategy and bullpen roles
Starters give length; relievers give leverage. Managers balance fatigue, handedness and how many times a hitter has already seen a pitcher.
Starter
Begins game and aims to provide multiple innings while navigating lineup repeatedly.
Opener
Short first pitcher used strategically before bulk innings from another pitcher.
Bulk reliever
Pitcher expected to cover multiple middle innings.
Setup reliever
High-leverage reliever used before closer, traditionally eighth inning.
Closer
Reliever commonly used to protect late leads, often in ninth.
Long reliever
Covers several innings when starter exits early or game goes long.
Left/right matchup
Pitcher-batter handedness can change pitch movement and platoon advantage.
Times through the order
Hitters often improve after seeing a pitcher multiple times; managers weigh this against bullpen quality.
Pitch count
Workload metric affecting fatigue and removal decisions.
Pitch sequencing
Ordering pitches to alter speed, eye level, location, and hitter expectation.
Tunneling
Different pitches travel similarly early before separating late.
Pitching backward
Using off-speed/breaking pitches in counts where fastball is traditionally expected.
Three-batter minimum
Since 2020 a reliever must face at least three batters (or finish the half-inning) unless injured, which ended the one-batter lefty specialist.
10TH · Strategy & stats
Situational strategy
There are exactly 24 base-out states: eight ways to arrange runners times zero, one or two outs. Each has a measured average number of runs that follow. That table explains modern strategy.
Run expectancy: the 24 base-out states
TAP A STATE · TEST A STRATEGYRunner on 3rd, less than 2 outs
Offense values any ball in play that can score runner; defense may play in.
Runner on 2nd, no outs
Offense may prioritize advancing runner; modern strategy varies by hitter quality.
Bases loaded
Force exists at every base. Walk/HBP scores a run.
Two outs
Runners can move aggressively on contact because a caught ball ends inning anyway.
Late lead
Defense prioritizes preventing extra bases; bullpen leverage increases.
Tie game late
Managers may emphasize matchup, bullpen, pinch runners, and one-run tactics.
Squeeze play
Bunt attempt designed specifically to score runner from third.
Intentional walk
Defense awards first base intentionally to change matchup or create force situation.
Pinch hitter
Substitute batter used for matchup or offense; removed player cannot return under MLB rules.
Pinch runner
Substitute runner used for speed or baserunning; replaces original player.
Defensive replacement
Better fielder enters late to protect lead.
Sacrifice bunt
Batter gives up likely out to advance runner; value depends heavily on context and run expectancy.
10TH · Strategy & stats
Statistics you actually need
Traditional stats count events; modern stats weight them by value and adjust for ballpark and era. The first three below are the foundation.
Slash-line calculator
AVG / OBP / SLG / OPSAVG
Batting average: hits divided by at-bats.
OBP
On-base percentage: (hits + walks + hit-by-pitch) ÷ (at-bats + walks + hit-by-pitch + sacrifice flies).
SLG
Slugging percentage: total bases ÷ at-bats (single = 1, double = 2, triple = 3, home run = 4).
OPS
OBP + SLG; simple combined offensive measure.
OPS+
League/park-adjusted OPS metric where 100 is league average.
wRC+
Comprehensive run-creation rate adjusted to league/park; 100 is average.
HR
Home runs.
RBI
Runs batted in; context-dependent counting stat.
SB
Stolen bases.
ERA
Earned runs allowed per nine innings: earned runs × 9 ÷ innings pitched.
WHIP
Walks plus hits allowed per inning pitched.
K/9
Strikeouts per nine innings.
BB/9
Walks per nine innings.
FIP
Fielding Independent Pitching; estimates outcomes tied more directly to pitcher: strikeouts, walks, HBP, HR.
WAR
Wins Above Replacement estimate combining contributions into one value; implementations vary.
BABIP
Batting average on balls in play, excluding HR and strikeouts from denominator structure.
ISO
Isolated power: SLG minus AVG.
Hard-hit rate
Share of batted balls above Statcast hard-hit threshold.
xBA / xSLG / xwOBA
Expected metrics based on quality/contact characteristics and other inputs.
Save
Relief pitching statistic awarded under specific qualifying conditions.
Hold
Credited to a reliever who enters in a save situation and leaves with the lead intact. Widely tracked, but not an official MLB statistic.
10TH · Strategy & stats
MLB The Show and baseball-game mode
The same count, sequencing and base-out logic wins in video games.
Play smarterTransferable habits
- Learn count leverage first. When ahead as pitcher, expand; when behind, prioritize strikes without becoming predictable.
- As a hitter, avoid chasing. Waiting for your pitch is usually more valuable than swinging at everything in the zone’s neighborhood.
- Sequence velocity and movement: hard inside can make soft away play up; breaking down/away can set up fastball above the zone.
- Know where double play exists. With runner on first and fewer than two outs, a ground ball can become two outs.
- Use defensive positioning and cutoff logic. Throwing directly to home is not always the right play.
- Baserunning mistakes are costly. Take the extra base only when ball location/arm situation gives a real edge.
- Manage bullpen by leverage, handedness, stamina, and who is due up, not only by inning labels.
Video-game interfaces and pitch ratings change by title/year. The goal is to teach transferable baseball logic.
Rulebook watch
New for 2026
MLB’s rules have changed more since 2023 than in the previous fifty years. Here is what is current for the 2026 season.
ABS challenge system in every game
Umpires still call balls and strikes, but the batter, pitcher or catcher can challenge immediately by tapping the helmet or cap, with no help from the dugout. Each team starts with two challenges and keeps any it wins; after two failed challenges it has none left. A team out of challenges gets one for each extra inning. The replay is shown on the videoboard.
A strike zone set by height
For ABS the zone top is 53.5% of the batter’s standing height and the bottom 27%, across the 17-inch plate. A pitch is a strike if any part of the ball touches that zone.
Pitch timer 15 / 18 seconds
15 seconds with the bases empty and 18 with runners on (it was 20 with runners in 2023). Violations are an automatic ball or strike.
Shift limits and bigger bases
Two infielders on each side of second base, all four on the dirt. First, second and third base grew from 15 to 18 inches square, shortening the distance between bases.
Two disengagements per plate appearance
Step-offs and pickoff throws are limited. A third unsuccessful attempt is a balk.
Reference
Baseball glossary
Every term from this page in plain English. Dotted-underlined words anywhere above also explain themselves when you hover or tap them.
- ABS
- Automated Ball-Strike system. In 2026 MLB uses it as a challenge system: players can appeal an umpire’s ball/strike call to Hawk-Eye tracking.
- Ace
- Team’s top starting pitcher.
- Around the horn
- Infield throw sequence or phrase for 5-4-3 double play style.
- Automatic runner
- The runner placed on second base to start each extra-inning half-inning.
- Backdoor breaking ball
- Breaking pitch starts outside and moves back over edge.
- Backstop
- Barrier behind home plate; sometimes colloquial for catcher.
- Balk
- Illegal pitcher action with runners on base resulting in penalty under rules.
- Barrel
- High-quality batted-ball classification.
- Base-out state
- The combination of which bases are occupied and how many outs there are, 24 in all.
- Batting order
- Fixed hitter sequence.
- Bleeder
- Weakly hit ball that finds a gap.
- Bullpen
- Relief pitchers and the warming area.
- Can of corn
- Easy fly ball.
- Check swing
- Hitter begins swing but attempts to stop; umpire judges whether it counts.
- Cleanup hitter
- Traditional fourth hitter.
- Cycle
- Single, double, triple, HR in same game.
- Dinger
- Home run.
- Disengagement
- A pitcher stepping off the rubber or attempting a pickoff. Limited to two per plate appearance.
- Double play
- Two outs on one continuous play.
- Dugout
- Team bench area.
- Error
- Fielder misplay judged to allow advancement that ordinary effort would have prevented.
- Exit velocity
- Speed of the ball off the bat, measured by Statcast.
- Extra-base hit
- Double, triple, or HR.
- Fielder’s choice
- Batter reaches because defense attempts to retire another runner.
- Frozen rope
- Hard line drive.
- Grand slam
- Home run with bases loaded.
- Green light
- Permission/encouragement to swing or steal in situation.
- Ground-rule double
- Awarded two bases under ballpark/universal ground rules.
- Hit-and-run
- Runner goes and batter swings.
- Hold runner
- Pitcher varies looks/timing to limit steal.
- In the hole
- Deep fielding area or upcoming hitter phrase depending context.
- Induced vertical break
- How much a pitch rises or drops compared with a spinless ball thrown at the same speed and angle.
- Infield fly
- Rule protecting runners from intentional dropped easy pop with force setup.
- Launch angle
- Vertical angle of batted ball.
- LOOGY
- Historic slang for a left-handed specialist reliever; the three-batter minimum (2020) ended the role.
- Mendoza Line
- Informal .200 batting-average reference.
- No-hitter
- No hits allowed by opposing team over qualifying game.
- Passed ball
- Catchable pitch not handled by catcher, allowing advancement.
- Perfect game
- No opposing batter reaches base in complete game.
- Pitch timer
- Clock limiting time between pitches: 15 seconds with bases empty, 18 with runners on.
- Pitchout
- Deliberate pitch away from hitter to help catcher throw out runner.
- Platoon
- Use players based on handedness matchup.
- Quality start
- At least six innings with no more than three earned runs.
- RBI
- Run batted in.
- Rubber
- Pitching plate.
- Run expectancy
- Average number of runs that score from a given base-out state to the end of the inning.
- Sac fly
- Flyout that scores runner and qualifies statistically.
- Save situation
- Game context that can qualify reliever for save.
- Shift
- Strategic fielder positioning. Since 2023, MLB requires two infielders on each side of second base with all four on the infield dirt at the pitch.
- Small ball
- Run-manufacturing style using bunts, steals, contact, advancement.
- Southpaw
- Left-handed pitcher.
- Strike zone
- Space over plate defined by rules and batter stance.
- Tag
- Touch runner with ball/glove containing ball when tag required.
- Take
- Do not swing.
- Texas leaguer
- Soft blooper between infield/outfield.
- Walk-off
- Game-ending hit/walk/etc. by home team taking lead in final inning/extra innings.
- Warning track
- Track near outfield wall.
- Wild pitch
- Pitch judged too difficult for ordinary catcher control, allowing advancement.
No glossary term matches. Try the ⌘K search for concepts.
Reference
Official sources
Rules and dimensions on this page follow these documents. Video-game notes teach transferable logic rather than edition-specific tricks. Page stats: 12 sections · 154 explained concepts · 11 interactive visuals · 58 glossary terms.
MLB Official Baseball Ruleswww.mlb.com/official-information/official-rulesMLB: ABS Challenge System coming to the Majors in 2026www.mlb.com/press-release/press-release-mlb-announces-abs-challenge-system-coming-to-the-major-leagues-beginning-in-the-2026-seasonMLB Glossary: Rules (pitch timer, shift, bases)www.mlb.com/glossary/rulesMLB Glossary: Statcast (barrel, exit velocity, launch angle)www.mlb.com/glossary/statcastBaseball Savant: pitch movement leaderboardsbaseballsavant.mlb.com/leaderboard/pitch-movementFanGraphs Library: RE24 / run expectancylibrary.fangraphs.com/misc/re24/
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