when can a player be substituted in soccer
Substitute (association football) A player may only be substituted during a stoppage in play and with the permission of the referee. The player to be substituted (outgoing player) must have left the field of play before the substitute (incoming player) may enter the field of play; at that point the substitute becomes a player and the person substituted ceases to be a player. The incoming player may only enter the field at the half-way line. Failure to comply with these provisions may be punished by a caution (yellow card).