Considering the violent attacks Trump encouraged against protesters, particularly those of color, at his rallies, any idiot would know it was only a matter of time before there was a backlash.
Of course, you can't let yourself believe everything you see...
Some were Trump protesters attacking supporters.
Some were actually supporters attacking protestors.
Some were total fakes, plants, brought in on buses and turned loose on the crowd to make the protestors look bad.
Bottom line - if the Trump fans weren't so brutal throughout his campaign, none of this would have happened yesterday.