What he will very likely be guilty of is threatening someone with lethal force when he didn't have a legal right to do so. I believe this is assault and since he kicked him likely battery also. This is a serious felony and you can lose your freedom if found guilty. Probably a good opening to a civil suite of "illegal detention" or whatever it is called in that state.
Technically it does not violate the rules. Is it highly unethical though.
The simple solution for the opposition would be to concede the putt for player A which means he then cannot putt it until everyone else has completed the hole and then it will be for practice only.