being assaulted

my son was beaten up rather badly outside a bar.he was too drunk to remember anything that happened.the person who hit him admits doing it,but saya my son hit him first.a witness who refuses to give a written statement says tha attack on my son was unprovoked.my question is-my son was badly beaten,the other guy doesnt have a mark on him.does it matter who really started it.the guy who beat my son up is presently on probation for assaulting someone outside the same bar.

The issue is does your son want to report it to the police and try to start a prosecution of the guy, and if so, would the police be interested given the difficulty of getting proof. That may depend on the other guy's record and how much they want to put him away.