You say they are public right of way, Morpheus says they are private land - who is right!
I don't know in this instance if the sidewalks are on public right-of-way or not. I suspect they are a public right-of-way, but again could not say for sure. My question to you is: Why does it matter so much? Assuming police responded to a scene on public property with a large and unruly crowd with reported violence, what do you expect them to do when individuals in the crowd fail to follow simple instructions to restore order and keep everyone safe while the disorder is still going on and police still have no idea who in the crowd, if anyone, represents a threat to anyone's safety? These police were not called to the scene because they had done something. The police were called to the scene because supposedly multiple individuals in the crowd had done something violent that was threatening safety. Were their knives? The police had no idea? Were their guns? The police had no idea. Until order was restored the police were having to look in every direction and suspect multiple individuals around them attempting to figure out what was going on.