Of course, by the time the video starts, there are several people involved in the fight.
The video starts after the fight has already begun (the one in the theater, not the one on the screen) so we miss whatever it was that instigated the event.
I guess it was probably one of each.
This could be a couple large groups who got into it or just a bunch of individuals who ended up on opposite sides, but it’s a fairly serious brawl.