A fourth official observes an offense worthy of a send-off during play, but it is not seen by either the referee or ARs. What can the fourth official do?
USSF answer (June 4, 2008):
We know from the Laws of the Game that the fourth official “assists the referee at all times.” The fourth official must also “indicate to the referee when the wrong player is cautioned because of mistaken identity or when a player is not sent off having been seen to be given a second caution or when violent conduct occurs out of the view of the referee and assistant referees” and also “has the authority to inform the referee of irresponsible behavior by any occupant of the technical area.” So it is clear that the fourth official has the authority to advise the referee in matters of game management and player control.
This is reinforced in the Guide to Procedures for Referees, Assistant Referees and Fourth Officials, where we learn that the fourth official “Notifies the referee as quickly as possible if a player or substitute has . . . committed violent conduct out of the view of the referee and assistant referees.”
The answer is analogous to the situation of the assistant referee who observes serious misconduct and begins to flag it before the ball next goes out of play; even though the game may have restarted before the referee sees the flag, the AR must keep the flag up (and call out, if necessary) to gain the referee’s attention.
In the situation you cite, the fourth official must do whatever is necessary and possible to gain the referee’s attention as quickly and expediently as possible. Depending on where each of the members of the officiating team is at the moment, it might be best for the fourth official to call to the referee directly, if he or she is nearby, or, if the senior AR is nearby, to use the AR’s means of communication to get the referee’s attention. Allowing too much time to pass while being polite and circumspect in notifying the referee would only worsen the inevitable tension between the players and lead to loss of control by the referee.