Honestly, I would recommend that you take a step back and look at what you've been writing. LSSpam laid it out pretty well I think, but you have not been very consistent in your comments. It actually is very confusing. You keep throwing out references to 12 Angry Men that don't make sense in this situation. Would juror 8 have been so gung-ho about "more backstory" if he was shown video footage of the kid stabbing his father?
We have this guy acting like a drunk fool, berating, bullying, hitting and picking fights with people who are trying to move away and clearly do not want to fight. If they called him a bad word (or whatever), it was over long before the video started rolling and they had backed down. Everything that happened after that was him being at fault. You have even said at least once that you agree with this, yet almost immediately go back to not wanting to accuse people (we don't know with what) without a backstory.
Several people have explained it better than me, but it's just not clear what you are looking for here. In your opinion, what could have happened right before the video started that would justify the guy's (the one who was knocked out) actions?