usually, from what ive seen, cops that try breaking up mobs dont succeed, because the protestors will turn it violent.
As a criminal justice major I need to disagree to an extent. There are steps a cop can make to shut down a protest no matter the size. It's up to the protesters to decide if they want to risk landing a lucky blow on a cop vs being gunned down. It's common sense really, don't mess with law authority and you won't get shot. You could argue that using extreme methods to subdue the crowd paints the enforcers as cruel, but if you've got a group of rowdy millennials charging at you at the speed of autistic screeching, chances are you're going to take lethal action as to not get hurt.
Some people suffer from shaken snowflake syndrome and don't like being ordered around by law figures, so it's likely that they're the ones to try and pull something stupid and end up dead.