The description of the video is a little ambiguous as to the reason why the fight was occurring.  Not sure why they were ganging up on the guy but just the way it was 4 people beating down 1 guy on the ground makes it seem like they deserved the ass kicking they got afterwards.

Also, to make it a bit less confusing - the guy in red shorts is the one initially getting beat down, an observer comes with beige shorts to help out, and those two are the ones fighting the rest of them.

Insane fight on Vegas Strip, crazy punches/kicks