1. In order to authorize the service, it is not necessary to check that the server is ready -- only that the player to serve is in possession of the ball. The first referee must whistle immediately.
In normal flow of the game (no substitution, no sanction, etc.) for FIVB, World and Officials Competitions, a duration of 15 seconds is available for service after the end of the previous rally. However, eight (8) seconds for the service is key, rather than 15 seconds – the first referee has discretion in the case of an exceptionally long rally to wait a little before whistling. This extends the time a little to allow players to recover.
2. Before the 1st referee whistles for service, he/she should check whether a re-play is requested by TV and should delay whistling; its frequency and duration may vary on different competitions accordingly.
3. The first referee and the corresponding line judges must pay attention to the position of the server at the moment of the service hit or take off for a jump service. The server may start his/her service motion outside the service zone but must be fully inside at the time of contact (or the foot making the final contact with the floor must be fully inside the service zone at the moment of the take-off).
4. When the ball is being served, the first referee must watch the serving team, while the second referee watches the receiving team.
5. If the server is not coming normally to the service zone or does not accept the ball from the ball retriever, making intentional delay, the team can receive a delay sanction. In order to avoid misinterpretation, the 8 seconds counts immediately after the first referee whistled for service.
6. The first referee should pay attention to screening during the execution of the service when a player or group of players of the serving team, waving arms, jumping or moving sideways or by standing grouped, prevent their opponent from seeing the service hit and flight path of the ball until the ball crosses the vertical plane of the net (i.e. both criteria need to be satisfied for player actions/ positions to be judged as a screen).
6.1. Tip: if you see the serving team player(s) attempt to prevent the receiving team player(s) from seeing the service hit after they have adjusted their position to see the server more clearly, this should heighten your awareness that a screen will be called if all of the conditions are met.
6.2. Tip: If the server jumps to serve the ball, then the receiving team can usually see the flight path of the ball.
6.3. If the served ball can be seen clearly throughout its path, until it crosses the net to the opponent, it cannot be considered as a screen.
7. The service cannot be authorized with whistle by the first referee if the team does not have the correct number of players (e.g. there are 5 or 7 players) on court. In such cases, he/she should wait and remind the team and, if necessary, should issue a delay sanction. A similar procedure should be applied if a libero rotated into the position 4 and clearly is not replaced by the respective player.