Baseball is a nine-a-side game played with bat, ball, and glove, mainly in the U.S.A. Teams consist of a pitcher and catcher, called the battery, first, second, and third basemen, and shortstop, called the infield, and right, centre, and left fielders, called the outfield. Substitute players may enter the game at any time, but once a player is removed he cannot return.
The standard ball has a cork-and-rubber centre wound with woollen yarn and covered with horse-hide. It weighs from 5 to 5 1/4 oz. (148 g.) and is from 9 to 9 1/2 in. (approx. 23 cm.) in circumference. The bat is a smooth, round, tapered piece of hard wood not more than 2 3/4 in. (approx. 7 cm.) in diameter at its thickest part and no more than 42 in. (1.07 m.) long.
Originally, fielders played barehanded, but gloves have been developed over the years. First basemen wear a special large mitt, and catchers use a large, heavily-padded mitt as well as a chest protector, shin guards, and a metal mask. Catchers were at first unprotected. Consequently, they stood back at a distance from home plate and caught pitched balls on the bounce, but the introduction of the large, round, well-padded mitt or "pillow glove" and the face mask enabled them to move up close behind the plate and catch pitched balls on the fly. Players wear shoes with steel cleats and, while batting and running the bases, they use protective plastic helmets.
The game is played on a field containing four bases placed at the angles of a 90-ft (27.4 m.) square (often called a diamond): home plate and, in counter-clockwise order, first, second, and third base. Two foul lines form the boundaries of fair territory. Starting at home, these lines extend past first and third base the entire length of the field, which is often enclosed by a fence at its farthest limits.
The object of each team is to score more runs than the other. A run is scored whenever a player circles all the bases and reaches home without being put out The game is divided into innings, in each of which the teams alternate at bat and in the field. A team is allowed three outs in each halfinning at bat, and must then take up defensive positions in the field while the other team has its turn to try to score. Ordinarily, a game consists of nine innings; in the event of a tie, extra innings are played until one team outscores the other in the same number of innings.
The players take turns batting from home plate in regular rotation. The opposing pitcher throws the ball to his catcher from a slab (called the "rubber") on the pitcher's mound, a slightly raised area of the field directly between home and second base. Bases are canvas bags fastened to metal pegs set in the ground.
The batter tries to reach base safely after hitting the pitched ball into fair territory. A hit that enables him to reach first base is called a "single," a two-base hit is a "double," a three-base hit a "triple," and a four-base hit a "home-run." A fair ball hit over an outfield fence is automatically a home run. A batter is also awarded his base if the pitcher delivers four pitches which, in the umpire's judgement, do not pass through the "strike zone" - that is, over home plate between the batter's armpits and knees; or if he is hit by a pitched ball; or if the opposing catcher interferes when he swings the bat. To prevent the batter from hitting safely, baseball pitchers deliver the ball with great speed and accuracy and vary its speed and trajectory. Success in batting, therefore, requires courage and a high degree of skill.
After a player reaches base safely, his progress towards home depends largely on his team mates' hitting the ball in such a way that he can advance.
Players may be put out in various ways. A batter is out when the pitcher gets three 'strikes' on him. A strike is a pitch that crosses the plate in the strike zone, or any pitch that is struck at and missed or is hit into foul territory. After two strikes, however, foul balls do not count except when a batter bunts - lets the ball meet the bat instead of swinging at it - and the ball rolls foul. A batter is also out if he hits the ball in the air anywhere in fair or foul territory and it is caught by an opponent before it touches the ground. He is out if he hits the ball on the ground and a fielder catches and throws it to a player at first base, or catches it and touches that base, before the batter (now become a base runner) gets there.
A base runner may be put out if, while off base, he is tagged by an opposing player with the hand or glove holding the ball, or if he is forced to leave his base to make room for another runner and fails to reach the next base before an opposing player tags him or the base; or if he is hit by a team mate's batted ball before it has touched or passed a fielder.
An umpire-in-chief "calls" balls and strikes from his position directly behind the catcher at home plate, and one or more base umpires determine whether runners are safe or out at the other three bases.