In association football, a substitute is a player who is brought on to the pitch during a match in exchange for an existing player. Substitutions are generally made to replace a player who has become tired or injured, or who is performing poorly, or for tactical reasons (such as bringing a striker on in place of a defender). Most competitions only allow each team to make a maximum of three substitutions during a game, although more substitutions are often permitted in non-competitive fixtures such as friendlies. Unlike some sports (such as American football or ice hockey), a player who has been substituted during a match may take no further part in it. A player who is noted for frequently making appearances, or scoring important goals, as a substitute is often informally known as a “super sub”.