Law 3 - Number of Players/Substitution/Injuries
Each team consists of 11 players, one of whom is the goalkeeper. A minimum of eight qualified players must be on the field to start a game. (Exception: for age groups U-17 and older, a minimum of seven qualified players is sufficient to begin a game.) If there are fewer than seven players on the field for a team, the game ends. (See exception for yellow-carded player.)
Unlimited substitutions can be made with the referee's consent prior to a throw-in, on a goal kick, after a goal, and at half time. Both teams may substitute prior to goal kicks, after a goal and at half time. As to throw-ins, however, only the team in possession has the initial option of so substituting, but if it does, the other team may also substitute as well. If the game is stopped to allow a substitution for an injured player, the other team may also substitute, on a one-for-one basis. No substitution is allowed prior to a corner kick. Note: no substitution can be made without the referee's consent.
A cautioned (yellow-carded) player must leave the field immediately, and a substitute may enter with the referee's consent. If that player's team has no substitutes, his/her team will play short-handed until its next substitution opportunity. If the yellow-carded team's player strength falls below seven, the game will still continue. Note: This BAYS rule for temporarily removing cautioned players is not intended to cause a game forfeit.
No sent off (red carded) player may re-enter the game nor may the player have a substitute.
All injuries that result in bleeding will be substituted for immediately. No bloodied player will return to the game unless bandaged, and blood-soaked uniforms cannot be worn.