SXSW Bully sucker punch. Justified or cheap?

Look up the definition of assault. Then look up the definition of battery.

If after doing that you do not believe the bully was guilty of each offense then don't bother with law school.

Regardless, that idiot had absolutely no reason to intervene the way he did. And should've gotten the same knockout. The 2 guys who "had enough" sure didn't show it now did they?