Guy who punched the other guy = FIRED
Guy who was punched = If so chooses, can press charges and/or sue for damages
I do not know the specific work comp laws concerning such a thing. I do know that generally with any work related injury or work comp case, those involved are usually drug tested first. This is a good way to keep from having to pay work comp to the employee and/or a reason to fire one. But this is mute as at least the attacker should be fired and possibly the "victim" suspended until an investigation of some sort. If the "victim" had, in fact, provoked the attack (I use provoked here loosely for the sake of time/detail) in some manner, he should be fired, too. However,
Now, a question for you. Are you one of these two guys? I ask because your post implies that perhaps you may be the supervisor of these two guys or something yet you don't know the workman's comp laws here? Sounds like one of those, "Well, I got this friend, and I, uhh, I mean, he did this thing, etc, etc.