In American football each team has 11 players on the field at one time. The specific role that a player takes on the field is called their position. Under the modern rules of American football, teams are allowed free substitutions; that is, teams may change any number of players after any play. This has resulted in the development of three "platoons" of players: the offense (the team with the ball, which is trying to score), the defense (the team trying to prevent the other team from scoring, and to take the ball from them), and the special teams (who play in kicking situations). Within those platoons, various specific positions exist depending on what each player's main job is.