After digging around it seems that indeed, police responded rather than initiated the violence. Allegedly the police complained that they were being pelted with stones and bottles, either as a form of provocation or as a response by the protesters for being removed from the park.
Now it is very simple you see, the local police have their own set of laws they follow and can react accordingly within the larger prism of the Constitution. So you may have a right to assemble, free speech and protest - but your right becomes impossible to perform if you attack a police offer because they have a right to restrain you. This is what happened, although the restraining was in the form of tear gas and flash bangs. Disproportional response? Possibly. However it is far from the one sided "policy brutality" nonsense we have been hearing all around. Perhaps the provocation worked as planned?
Here is a video of an Oakland protester admitting that the police were indeed being pelted with objects.


