As far as I can see, that kid did nothing to deserve getting hit. Looks like he was just dancing.
Since Jay did the punching, it is cool cause he is a punk rock god. Had someone in the audience punched him or anybody else, they would be an asshole for ruining the show.
As for walking off the stage after 3 songs. That is to be expected at any $12 Jay Reatard show.
I am not a Jay Reatard fan. But in his defense, I will say the fighting...who gives a fuck? It's a punk rock show. Aggressive music mixed with booze. It's bound to happen. Punk has no balls these days.