From an anonymous iSteve commenter:
Watching a lot of these videos and reading accounts, it tends to come down to groups of protesters who are told to disburse after a declaration of unlawful assembly by the cops, they don’t, the cops tolerate it for a while while continuing to tell them to disburse, and then a half hour later come gas and rubber bullets. At the moment that happens, yes, the crowd is not doing anything different than they had been doing five minutes before: they had simply been continuing in a “mostly peaceful” violation of a police order.
This is basically a group white version of the individual black conduct of “I don’t feel like being arrested today” thing. If a cop tells you he is going to arrest you, that’s what is going to happen, and you can make it easy or make it hard (and maybe get killed if you force them to sit on you or shoot you). Likewise, if the cops tell you they are going to clear the streets, that’s what’s going to happen, and you can leave then, or you can wait around and maybe take a supersonic Nerf ball to your testicles later.
Someone should redo Chris Rock’s video for mass protests.
Another factor in mass assemblies is the menace factor of groups: Police have to take into account that they are outnumbered and if don’t show some potentially injurious force to deter the bulk of the crowd the police themselves can be put in danger.