Which action is considered a proper substitution?

The action of a substitute entering after the second referee's indication is crucial in volleyball officiating. This ensures that the substitution process is conducted in accordance with the rules of the game. When the referee signals for a substitution, it is their responsibility to confirm that the outgoing player has completed their exit and that the incoming player is ready to take their place. This procedure maintains the flow of the game and ensures that the substitution is recorded accurately.

Following the referee's signal is essential, as it upholds the integrity of the match and prevents any potential confusion on the court regarding player rotations. Proper communication and adherence to signals help maintain the game's structure and ensure that all players are in compliance with the rules during substitutions.

The other options describe scenarios that deviate from the standardized procedure, which can lead to confusion and improper enforcement of the substitution rules.