Your example is flawed because you're comparing arresting one person opposed to multiple people. In any situation police officers ALWAYS want to outnuraber the subjects. Hence why you'll see two/three cop cars behind a pulled over vehicle. In this case they need to remove and possibly arrest 20 or so people. Yes, they're non-violent, but they're still directly disobeying a direct order. In a perfect world they could just arrest them, but in law enforcement you don't pussy foot around and take a situation for granted. You have to assume the worst and as such it's in your best interest to incapacitate the group before you arrest them instead of have them fully functioning.