FIDE and USCF: If an arbiter is watching a chess game and observes that a rule has been violated, should the arbiter intervene? Or should the arbiter intervene only if a player complains? Some people would think that if the arbiter intervenes, he/she would be making noise and interrupting the entire chess tournament. On the other hand, some people would think that if the arbiter does not intervene, he/she would not be fulfilling his/her role, like a police officer who sees a crime and does not stop it. On the other hand, this situation would not be a crime but a violation of a rule. They are not the same. What do the rules say about this situation?
The arbiter must intervene
In a Fide event, the arbiter is supposed to intervene and make sure that the rules are respected.
From FIDE Handbook :
Article 12: The Role of the Arbiter (see Preface)
12.1 The arbiter shall see that the Laws of Chess are observed.
12.3 The arbiter shall observe the games, especially when the players are short of time, enforce decisions he/she has made, and impose penalties on players where appropriate.
12.6 The arbiter must not intervene in a game except in cases described by the Laws of Chess. He/She shall not indicate the number of moves completed, except in applying Article 8.5 when at least one flag has fallen. The arbiter shall refrain from informing a player that his/her opponent has completed a move or that the player has not pressed his/her clock.
The arbiter is the only one (beside the players) who can interfere:
12.7 If someone observes an irregularity, he/she may inform only the arbiter. Players in other games must not to speak about or otherwise interfere in a game. Spectators are not allowed to interfere in a game. The arbiter may expel offenders from the playing venue.
I once witnessed a player, whose opponent was away from the board, play a move, notice that it was a mistake, take it back and play something else - which is obviously illegal. Although his opponent had seen nothing of it, the arbiter had noticed the take back and stepped in to ensure the position was corrected back with the move that was first played.
I have no idea about specific USCF rules, but if a USCF-led tournament is FIDE-rated, I expect the Laws of Chess to be enforced.
A necessary condition for a game to be rated by FIDE is that it shall be played according to the FIDE Laws of Chess.