If a referee crew is short a referee at game time - NO 2 whistle system!
The diagonal system of control consists of one referee and two assistant referees. All competitions sanctioned by the U.S. Soccer Federation require the use of this officiating system and certain competitions may require the use of a fourth official.
In order to comply with the Laws of the Game all games sanctioned directly or indirectly by member organizations of the U.S. Soccer Federation must employ the diagonal system of control and be assigned according to the following order or preference:
- One registered referee and two registered assistant referees
- One registered referee, one registered assistant referee and one unregistered club linesperson*
- One registered referee and two unregistered club linespersons*
- One registered referee only if no unregistered club linespersons are available or if one registered referee is appropriate for the level of competition
*Club linespersons are only allowed to signal for the ball in and out of play. The preference should always been given to unregistered club linespersons who have no affiliation to the participating teams".