Good question. The Masters has a lot of officials (At least 3 on each hole) so it's pretty unlikely that something goes unnoticed. Also, a lot more people are watching the Masters so if someone watching at home noticed something, they would have already called in by now. IIRC... once the player sign and turn in their scorecard over in that tent after the round is final. Otherwise the player would be DQ because he signed a lower score on that hole (if a penalty occurred). I believe, in this case, that the player would still win because PGA will be like, "Yes, this player made a penalty on this hole, but nobody caught it before he turned in his card so the score stays the same." A lucky break type of deal unless they can somehow prove the player knew of the penalty and didn't account for it then he's DQ and lose the win. Golf is weird in that players are in charge of penalizing themselves. So if the player signed a scorecard with a score lower than what it should be they would be DQ. The PGA doesn't have to prove that the player didn't know it was a penalty. The players are supposed to know the rules. They can't claim ignorance. What they would do is tell the player that someone said they should be penalized and adjust their scorecard before they turn it in. In a major tournament, the type of people that live for that horsefeathers are all watching and will call in immediately. That's the difference with the Lexi Thompson situation- not as many people are watching some random women's tour event.