Each team during a game of football is able to make up to three substitutions. In association football a substitute is a player brought onto the field for an existing player, generally because they are tired, fatigued or under performing. A player may only be substituted when the play stops and the referee gives the signal to notify they are allowing this to happen. The player must only enter the field at the half way line and wait for their team-mate to leave the football pitch. The player who has left the field is not allowed to return to the pitch for the duration of the match.
In a game situation if a key player becomes injured and is unable to play due to the fact that this will cause further injury, then a substitution can be made. The player may have already left the pitch for a few minutes to try and recover, therefore another player can fill their position as a substitute. Otherwise, the substitution process if followed where the player has to leave the field, the time lost is then totted up and added on at the end of the game as ‘injury time’. An official at the sideline will hold up a substitution board with the number of the player who is coming off and the number of the new player. The names of the players will then be announced over the speaker and applause is given by the crowd for their contribution to the game.