Who may whistle, and in what order do referees signal after a fault?

From the FIVB Rules 2025-2028 (Rule 22.2). Only the 1st and 2nd referees may blow a whistle during the match. The 1st referee whistles to authorise the service that begins the rally. Either referee whistles to end the rally, but only when sure a fault was committed and its nature identified. They may also whistle while the ball is out of play to authorise or reject a team request.

Immediately after the whistle that ends the rally, the referees use the official hand signals:

• Fault whistled by the 1st referee: show in order (a) the team to serve, (b) the nature of the fault, (c) the player at fault, if necessary.
• Fault whistled by the 2nd referee: the 2nd referee shows (a) the nature of the fault and (b) the player at fault, if necessary, then (c) the team to serve following the 1st referee's signal. The 1st referee shows only the team to serve, not the fault or the player.
• Attack hit or blocking fault by back-row players or the Libero: both referees indicate, following the sequences above.
• Double fault: both referees show the nature of the fault and the players at fault, if necessary, in order, and the 1st referee then indicates the team to serve. The rally is replayed.

The 2nd referee may signal faults outside their own range without whistling, but may not insist on them to the 1st referee.