A team has a player red carded in the first half. After 20 minutes of play in the second half, the referee is alerted by a coach that the offending team has 11 players on the field, clearly adding one at half time.
What is the call?
USSF answer (February 25, 2008):
While the fault certainly lies with the referee and the rest of the officiating team, who have failed in their duty to enforce the Law, something must be done about the extra player. You will find full details in the USSF publication “Advice to Referees on the Laws of the Game,” which may either be downloaded or purchased in soft cover form from the US Soccer Federation website at www.ussoccer.com. Here is a brief description of what must be done in the situation you describe:
In all cases, play must be stopped and the extra person identified and removed from the field. Other than through referee error, this situation can occur only if someone enters the field illegally. In addition to the punishment and restarts listed below, the referee must include full details in the match report. Furthermore, all actions by the team with the extra player which occurred prior to the stoppage for the extra player will stand, with one exception: If the game was stopped for a goal by the team with the extra player (who was then discovered at that stoppage), that goal is not scored.
If the “extra player” is an outside agent (such as a previously expelled player or a spectator), the game is restarted with a dropped ball at the place where the ball was when play was stopped.
If the “extra player” is a substitute (and on the team’s roster if rosters are required by the rules of the competition), that substitute (or substituted player) is cautioned for unsporting behavior and the game is restarted with an indirect free kick for the opposing team from the place where the ball was when play was stopped.