This is an almost literal repetition of what happened in Washington DC (I don't remember just when, but no doubt somebody can find it). The KKK (I think) was planning a rally on the Mall, for which they had a permit. Because of the threat of violence by opponents of the Klan, the rally was called off, whereupon the "counter-demonstators" attacked people and property near the Mall. Later a civic leader had the gall to blame the police for the violence, because they allowed the rally, even though the rally didn't happen.
These leftists hate the police. If there are police present "restraining" rhe "counter" protesters (really protesters of a different stripe, they continue to protest even when there is nothing to counter) they take it as just cause to riot.
What about jury verdicts they dislike?
Loot, burn, rob, kill. Same thing isn't it?