You are wrong if you wait for someone to punch you before you retaliate. You're assuming all the risk in a self defense situation. You gonna let some dingbat stab you first too?
Gavin probably should have walked away. The other dumbass definitely should've walked away. If the storyline holds true I hope the charges against Gavin are dropped entirely. If it makes it to court I hope his charges are acquitted by the jury.
Dude with a broken jaw should equally be charged with crimes...disorderly, disturbing the peace, harassment, heck I'd like to see a charge for assaulting Gavin's fist with his face.
I'm not for violence but I'm even moreso against rewarding degenerates for being degenerate. The guy took it upon himself to place himself in a risky situation, own it.
What's legal is a different matter unfortunately.