Substitution are carried out in the substitution zone (center line to attack line). A player, ready to play, must enter the substitution zone to request a substitution. The second referee authorizes the substitution by the offical hand signal.
In the case of a multiple substitution, the other players must be ready to play near the substitution zone at the time of the substitution request made by one player. If this is not the case, it is a question of two substitution requests from one team in succession. Consequently, the second substitution request is rejected by the second referee.
Each team is entitled to 'six regular substitutions per set. Players from the line-up may be substituted out and substituted in. After that they are not allowed to participate in any regular substitution, but in exceptional substitutions. Substitute player may be substituted in and out. After that they are not allowed to participate in any regular substitutions, but exceptional substitutions. All substitutions must be recorded in the score sheet.
Any player (except the libero) may be exceptionally substituted when he is no longer able to continue playing due to injury or illness, 'when no regular substitution is possible. Any player who is not participating in the match at that time (except the liberos or the replacement player) can be subject to the exceptional substitution. The exceptionally substituted player may no longer take part in the match.
The exceptional substitution is not recorded in the set itself, but counted in the Results-area.
The substitution request happens when the substitution player(s) enter(s) the substitution zone. If a request is made after the authorization for the next service, or if other players arrive late for a substitution, this must be rejected and an improper request has to be recorded in the score sheet. The same applies to the request for a seventh substitution.
An illegal substitution is, if, for example, a substitution in which a player is substituted for another player and then substituted for another player; i.e.: player 3 is substituted for player 7, a few points later player 3 is substituted for player 1. The same applies to the attempt to substitute player 3 out of the game, player 3 into the game, player 3 out of the game. These requests are to be punished with a sanction according to the progress on the sanction scale for delays.
If an illegal substitution has occurred without the referees having noticed at the time of the substitution, the following procedure must be followed immediately upon notice: The illegal substitution must be canceled and all points scored by the team since the illegal substitution are deducted from the score. The points of the opposing team shall be retained. The opposing team also receives the service right and one point.