A simplified version of the rules of baseball is at simplified baseball rules. The complete Official Rules can be found www.mlb.com, the official web site of Major League Baseball in the United States.
Baseball is played between two teams of nine players each on a baseball field, under the authority of one or more officials, called umpires. There are usually four umpires in major league games; up to six (and as few as one) may officiate depending on the league and the importance of the game. There are four bases. Numbered counter-clockwise, first, second and third bases are cushions (sometimes informally referred to as bags) shaped as 15 in (38 cm) squares which are raised a short distance above the ground; together with home plate, the fourth “base,” they form a square with sides of 90 ft (27.4 m) called the diamond. Home base (plate) is a pentagonal rubber slab known as simply home. The field is divided into two main sections:
- The infield, containing the four bases, is for defensive and offensive purposes bounded by the foul lines and the grass line (see figure). However, the infield technically consists of only the area within and including the bases and foul lines.
- The outfield is the grassed area beyond the infield grass line (for general purposes; see above under infield), between the foul lines, and bounded by a wall or fence. Again, there is a technical difference; properly speaking, the outfield consists of all fair ground beyond the square of the infield and its bases. The area between the foul lines, including the foul lines (the foul lines are in fair territory), is fair territory, and the area outside the foul lines is foul territory.
The game is played in nine innings (although it can be played with fewer, such as it is in little league) in which each team gets one turn to bat and try to score runs while the other pitches and defends in the field. An inning is broken up into two halves in which the away team bats in the top (first) half, and the home team bats in the bottom (second) half. In baseball, the defense always has the ball — a fact that differentiates it from most other team sports. The teams switch every time the defending team gets three players of the batting team out. The winner is the team with the most runs after nine innings. If the home team is ahead after the top of the ninth, play does not continue into the bottom half. In the case of a tie, additional innings are played until one team comes out ahead at the end of an inning. If the home team takes the lead anytime during the bottom of the ninth or of any inning thereafter, play stops and the home team is declared the winner.
A batter follows through after swinging at a pitched ball.
The basic contest is always between the pitcher for the fielding team, and a batter. The pitcher throws—pitches—the ball towards home plate, where the catcher for the fielding team waits (in a crouched stance) to receive it. Behind the catcher stands the home plate umpire. The batter stands in one of the batter’s boxes and tries to hit the ball with a bat. The pitcher must keep one foot in contact with the top or front of the pitcher’s rubber—a 24″ x 6″ (~ 61 cm x 15 cm) plate located atop the pitcher’s mound—during the entire pitch, so he can only take one step backward and one forward in delivering the ball. The catcher’s job is to receive any pitches that the batter does not swing at or swings at and misses and to “call” the game by a series of hand movements that signal to the pitcher what pitch to throw and where. If the pitcher disagrees with the call, he will “shake off” the catcher by shaking his head; he accepts the sign by nodding. The catcher’s role becomes more crucial depending on how the game is going, and how the pitcher responds to a given situation. Each pitch begins a new play, which might consist of nothing more than the pitch itself.
Each half-inning, the goal of the defending team is to get three members of the other team out. A player who is out must leave the field and wait for his next turn at bat. There are many ways to get batters and baserunners out; some of the most common are catching a batted ball in the air, tag outs, force outs, and strikeouts. After the fielding team has put out three players from the opposing team, that half of the inning is over and the team in the field and the team at bat switch places; there is no upper limit to the number that may bat in rotation before three outs are recorded. Going through the entire order in an inning is referred to as “batting around”. It is indicative of a high scoring inning. A complete inning consists of each opposing side having a turn (three outs) on offense.
The goal of the team at bat is to score more runs than the opposition; a player may do so only by batting, then becoming a base runner, touching all the bases in order (via one or more plays), and finally touching home plate. To that end, the goal of each batter is to enable baserunners to score or to become a baserunner himself. The batter attempts to hit the ball into fair territory—between the baselines—in such a way that the defending players cannot get them or the baserunners out. In general, the pitcher attempts to prevent this by pitching the ball in such a way that the batter cannot hit it cleanly or, ideally, at all.
A baserunner who successfully touches home plate after touching all previous bases in order scores a run. In an enclosed field, a fair ball hit over the fence on the fly is normally an automatic home run, which entitles the batter and all runners to touch all the bases and score. A home run hit with all bases occupied (‘bases loaded’) is called a grand slam.