I expect it's rare to find BLM protestors undermining their own movement with violence, giving the police an excuse to crack down, and the right confirmation that the demonstrators are all violent hooligans.
The ones that want violence and enjoy confrontations are right-wing radicals like the Proud Boys, Boogaloo Boys and other Neo-Nazi, Black Bloc or white supremacist groups. They're drawn to demos like moths to a flame.
The police, on the other hand, are obsessed with order and control. Disorderly people p*ss them off and, in their eagerness to take charge of the situation, they end up inciting the very violence they claim they're there to prevent. Nor are they above a little punitive violence themselves, if they think they're not being filmed.
And, of course, both right radicals and the police are not above a little covert provocation.
Agent Provocateurs: Police at Protests Caught Destroying Property