Defense (sports)

In many team sports, defence or defense is the action of preventing an opponent from scoring. The term may also refer to the tactics involved in defense, or a sub-team whose primary responsibility is defense. Similarly, a defense player or defender is a player who is generally charged with preventing the other team's forwards from being able to bear down directly on their own team's goalkeeper or goaltender. Such intentions exist in association football, ice hockey, water polo and many other sports.

In ice hockey, there are normally two defencemen on the ice. One is usually a more offensive player better known for their ability to glean assists or goals rather than for their strong defensive play. Such players are known as offensive defencemen. The other is usually in a more defensive role and rarely show-up on the score sheet but are important for their defensive prowess; these players are known as stay-at-home defence.

In water polo, if an offensive player, such as the center forward, has the ball in front of the goal, and the defender cannot steal the ball, he may intentionally commit a foul. The forward then has a free throw but must pass the ball off to another offensive player, rather than making a shot at the goal. Defensive perimeter players may also intentionally cause a foul and then move toward the goal, away from their attacker, who must take a free throw. This technique, called 'sloughing', allows the defense an opportunity to double-team the center forward and possibly steal the inbound pass. The water polo referee may refrain from declaring a foul caused by a defensive player, if in his judgment this would give the advantage to the defending team. This is known as the Advantage Rule.

Baseball is unlike most other competitive sports in that the defense is given control of the ball. Additionally, the number of players on the field at any given time is in favor of the defense which always has nine players on the field; the offense has between one and four.

Historically, each player on the team had a role both on offense and defense. Most amateur and professional leagues have adopted the designated hitter (DH) rule introduced by the American League of Major League Baseball. In leagues that use the DH, pitchers usually do not bat, and the DH bats in lieu of the pitcher and does not play a defensive position. The main leagues that have not adopted the DH rule are the National League of MLB and the Central League of Nippon Professional Baseball.

...
Wikipedia