I found the video of the Shapiro speech that started it. I haven't watched the whole thing (and probably won't) but it got to the place where he went after the "alt right".

The violence baffles me. It's as if somebody on the left heard Trumps encouraging beating up dissenters and saw some of his peeps doing that, and said "Oh, I hate that. Let's do it to THEM." Just a case of becoming what they hate.