Like I said, crowd control is a science. Even if you have violent actors at the protest, it is still a failure of crowd control if the whole protest turns violent.

Reacting when violated is a natural reaction. With a group this big you cannot think in individual terms. If provoked there and there is a non-zero chance you’ll see a reaction, you will see a reaction. And now you have a positive feedback loop between the police and protestors that may escalate into riots.