Copied directly from the USGA rule book: 23-1/2 Large Stone Removable Only with Much Effort
Q. A
player’s ball lies in the rough directly behind a loose stone the size
of a watermelon. The stone can be removed only with much effort. Is it
a loose impediment which may be removed?
A. Yes.
Stones of any size (not solidly embedded) are loose impediments and may
be removed, provided removal does not unduly delay play
(Rule 6-7). Doesn't seem fair but that is the ruling; in regard to assistance that is also covered:
23-1/3 Assistance in Removing Large Loose Impediment
Q. May spectators, caddies, fellow-competitors, etc., assist a player in removing a large loose impediment?
A. Yes. So Tiger (or anyone else that can get enough people) can legally cheat and not feel bad about it....the ruling is odd to say the least.