Each U10 and older game requires an AYSO-certified three-person referee crew on the field. The crew consisting of a referee and two assistant referees. In the event that one or both assistant referees are not available, the home-team coach should provide club linesmen, whose job is to call when the ball crosses the touchline.
All referees need to register as volunteers every year. Most certifications only need to be taken once, but a few may need bi-annual or yearly reviews.