He who is without sin can cast the first stone. Punish him and hold him accountable. Ruining his life for this is just dumb and despite fans being blinded by the rivalry, it won't happen unless he gets some idiot judge. You can obtain justice and accountability without destroying someone's life for this.
If he threw a metal water container, that is a lot more serious.
Teenagers at 18 are dumb. Yes. Adults are dumb too for those that get hung up on that. I would be shocked if there weren't 30 something year olds throwing large objects too - they just missed.