if those dumb ass know that what they do will trigger the fire in the large crowd , and they still do that. They need to accept the consequence (certain people in the crowd may have violent body contact or personal insulting). What the cop can do is bringing those small crowd of dumb ass out of the LARGE crowd in order to protect both parties, and the people who are in NO PARTY (i.e. families with children and oldies)
if u think the cop should use force to stop the large crowd from being angry and acting offensive to those small crowd instead of bringing away the small handful of people is the right way to prevent conflict at that moment, as another member (forgot the name) said, ok, you win