Baseball

Baseball is a bat-and-ball team sport played on a fan-shaped field between two nine-player squads that alternate offence (batting) and defence (fielding). Each half-inning ends when the fielding side records three outs; a full inning is one half from each team and a regulation game is nine innings, extra innings played if tied. The batter tries to hit a pitched ball into fair territory and complete a circuit of four bases (first, second, third, home) to score a run. The modern game codified rules first published in 1845 in New York by Alexander Cartwright and grew from earlier bat-and-ball games such as rounders. It is the most popular team sport in the United States (Major League Baseball), Japan (Nippon Professional Baseball), South Korea (KBO), and much of Latin America (Cuba, Dominican Republic, Venezuela).

Runs are the only scoring unit — recorded each time a runner completes the circuit of bases legally.

Win condition · Team with more runs after 9 innings wins. If tied, extra innings are played until one team leads at the end of a complete inning.

A fan-shaped field with a 90-ft square infield (the 'diamond'), a pitcher's mound in the middle, and an outfield beyond. Foul lines from home plate through first and third bases define fair territory.

• Baseball

  Cork-and-rubber core wound with yarn and covered in cowhide leather; 5-5¼ oz (142-149 g), circumference 9-9¼ in.

• Wooden bat

  Solid wood (ash, maple, birch) — MLB requires wood; college and amateur allow metal alloys.

• Fielding glove

  Leather glove worn on the non-throwing hand; position-specific designs (catcher's mitt, first baseman's mitt, infielder's, outfielder's).

• Batting helmet

  Mandatory for batters and base runners.

• Catcher's gear

  Mask, chest protector, shin guards — required for the catcher.

• Cleats

  Metal or moulded studs for grip on grass and dirt.

• Pitcher (P)

  ×1

  Throws pitches to the batter from the mound.

• Catcher (C)

  ×1

  Squats behind home plate, receives pitches, calls the game.

• First baseman (1B)

  ×1

  Fields at first base; receives throws for putouts.

• Second baseman (2B)

  ×1

  Fields right of second base; turns double plays.

• Third baseman (3B)

  ×1

  Fields at third base; strong throwing arm.

• Shortstop (SS)

  ×1

  Fields between 2B and 3B; the athletic anchor of the infield.

• Left / Center / Right fielder (LF/CF/RF)

  ×3

  Outfielders — catch fly balls and back up throws.

• Designated hitter (DH)

  ×1

  Bats for the pitcher (or another position); does not field.

The home-plate umpire calls balls and strikes and rules on plays at home; base umpires call safe/out on force and tag plays. MLB uses instant replay review for most calls except balls and strikes.

• Home-plate umpire
• First-base umpire
• Second-base umpire
• Third-base umpire
• (Postseason: LF & RF line umpires)

• Small ball

  Bunts, hit-and-runs, sacrifice flies — manufacture one run at a time.

• Launch angle / three true outcomes

  Modern MLB emphasis on home runs, walks and strikeouts driven by Statcast analytics.

• Shifting

  Positioning fielders based on batter tendencies; MLB limited infield shifts in 2023 (2 infielders per side of 2B).

• Bullpen management

  Using relief pitchers matched to specific batter platoons; openers and 'follower' rotations.

Strike

A pitch in the strike zone not swung at, or any pitch swung at and missed or fouled (foul balls only strike 1 and 2).

Ball

A pitch outside the strike zone not swung at.

Walk (BB)

Four balls — the batter takes first base free.

Strikeout (K)

Three strikes recorded on the batter.

RBI

Run batted in — credit given to the batter for a run scored on their at-bat.

ERA

Earned run average — average earned runs a pitcher allows per 9 innings.

OPS

On-base plus slugging — sum of a batter's on-base and slugging percentages.

Bullpen

Area where relief pitchers warm up; also refers to the relievers themselves.

Double play

One continuous play in which two runners are put out.

Grand slam

A home run with all three bases occupied — scores 4 runs.

Perfect game

A pitcher retires all 27 batters without any reaching base — extremely rare (24 in MLB history).

Cycle

A batter hitting a single, double, triple, and home run in the same game.

• MLB World Series

  annual · USA/Canada · since 1903

• World Baseball Classic

  quadrennial · worldwide · since 2006

• Summer Olympic Games

  quadrennial · worldwide · since 1992

  In-out sport; returned in Tokyo 2020, dropped for Paris 2024, back for LA 2028.

• Nippon Series

  annual · Japan (NPB) · since 1950

• Korean Series

  annual · South Korea (KBO) · since 1982

• Caribbean Series

  annual · Caribbean · since 1949

• 🇺🇸United States
• 🇯🇵Japan
• 🇰🇷South Korea
• 🇹🇼Taiwan
• 🇨🇺Cuba
• 🇩🇴Dominican Republic
• 🇻🇪Venezuela
• 🇲🇽Mexico
• 🇵🇷Puerto Rico
• 🇨🇦Canada
• 🇳🇱Netherlands
• 🇮🇹Italy
• 🇦🇺Australia
• 🇳🇮Nicaragua
• 🇵🇦Panama

• Major League BaseballMLB

  Founded 1903 · New York City, USA

  Official site ↗

• World Baseball Softball ConfederationWBSC

  Founded 2013 · Lausanne, Switzerland

  Official site ↗

• Nippon Professional BaseballNPB

  Founded 1936 · Tokyo, Japan

  Official site ↗

• Korean Baseball OrganizationKBO

  Founded 1982 · Seoul, South Korea

• Wikipedia — Baseball— Wikipedia
• Official Baseball Rules (MLB)— Major League Baseball
• World Baseball Softball Confederation— WBSC