The lesson of this video is: don't fuck with Sacramento. The frontman of the band Smack'd Up tried to get the local crowd amped up by turning heel on them, and moshing Santa in the pit would have none of it, so he ran up on stage and smacked the dude down. Comedy ensues.
If you're curious what the ironically-named Smack'd Up sound like:
[Thanks for the tip, Jack C.]