Each club contracts a squad of 16 Youth Development Players. Players must be between the ages of 16 and 21 as of 1 January in the year the season commences. Four over-age players (including goalkeeper) are also allowed to be selected (except when playing the AIS where it is restricted to two), usually these coming from the senior team. Each youth player must receive a minimum of 30 minutes game time. Players under 21 signed for the first team filling foreign player spots are classed as over-age players.These players can be any Australian player within the age group. A-League clubs must draw replacement players for their senior teams from the Youth League squad, except under certain circumstances. Such would include severe injuries to over-age players where an injury replacement player is able to be signed.