HighCheese: Do not run from this. You have done nothing wrong. The AD should know about this and do NOT let him sweep it under the rug. I repeat my former assertion: there should never be physical contact intitiated by a player or coach at ANY level. It is called simple assault and the law addresses the subject quite clearly.
Just wanna play a thought exercise...
If this altercation had been between your son and his minor league manager, would you stick with your advice?
I would give the team a shot at doing the right thing. If they did not, then I would hire an attorney. Professional in any category of life does not give someone free reign to break the law.The same applies to the player who has no right to assault a coach, official, GM etc.