Defense ( sport ) In many team sport s , defense or defence ( see spelling differences ) 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 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 . Such intention exist in association football , ice hockey , water polo and many other sports . By sport . Ice hockey . In ice hockey , there are normally two defensemen 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 defenseman " . 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 defense " . Water polo . 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 . Baseball is unlike most other competitive sport in that the defense is given control of the ball . Additionally , the number of players on the field at any given time is lopsided in favor of the defense 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 . Each play starts with the ball in the hands of the pitcher , whose job as a member of the defense is to use his skills to somehow prevent the batter from reaching base . The pitcher throws the ball toward the catcher , whose must catch the pitched ball if it is not hit by the batter . In each half - inning , the defense attempts to force three outs . There are three basic ways in which an out can occur : 1 . ) If three strikes are recorded against the batter , 2 . ) if a ball hit by a batter is caught by a defensive player before it hits the ground , or 3 . ) if a runner who is between bases or has not reached a base to which he is forced is put out by a defensive player in possession of the ball . If the batter manages to hit the ball , all nine defensive players become active and use the ball in attempting to prevent the batter from reaching base and runners already on base from advancing or scoring . While the offense is busy attempting to move runners around the baseball diamond toward home plate , the uses the ball in various ways to achieve outs . If the defence forces three outs , their team is moved into the offensive role . The exception is if it is the ninth or an extra inning and they are ahead , in which case , the game ends and the defensive team wins .