aguahombre, on 2015-July-17, 05:58, said:
You are preventing the establishment of a revoke -- a separate irregularity. You may or may not be drawing attention to an irregularity already committed. Maybe he actually was out of the suit.
Some irregularities cannot be legally prevented, revoke is one of them because you cannot know that a revoke is in progress until it is actually committed. You don't even then know if it is a revoke until you have verified whether he is really void in the suit. And that is where Law 61 is relevant. It does not allow a player to prevent a revoke from being committed but it allows him to prevent it from becoming established.
However, if you for instance notice your partner (or any player) about to pull a card from his hand when you know it is not his turn to play you have every right to stop him in the act.