Ok, long story short (as possible):
Some hardcore dudes showed up at a local show and started to beat the shit out of a metal dude who was asking why they were fighting. They were the pricks that do the kickdancing shit and start fights for the hell of it. So about 10 dudes jump this one metalhead, and the metalhead wasn't doing shit back, but he gets kicked out of the club. Then one of the bands is playing (drown mary) and one of the douchebags starts to try and start shit with one of the members of the band while they are on stage. So he jums off the stage onto the dude, then gets back and finishes the song, then the hardcore kids all got onstage to beat the shit out of the band. The "security" let it all happen because they are friends with the dudes who did it. It is a group, not all hardcore kids do that, but still it is bullshit.