The guy had no weapon,spiting on someone then the other person hitting him with a bottle is excessive force. I don't blame the guy,morally it's justified but legally he is probably guilty. If he is convicted at trail he can be facing years in jail,the plea deal might be his best option. Maybe he can arrange a few months,house arrest,the worse part might be having a felony especially a violent on his record. Also if found guilty at trail he probably gonna be sent to state jail or whatever it is,a few months at county isn't as bad.
He should ask his lawyer what his chance at trail is,if this is the best deal he can get.It sounds like he should take it,the lawyer is the best person to advise him.

