Richard Spencer is a very provocative and controversial figure. He's denied that he is a neo-Nazi, but he has expressed undoubtedly white supremacist views and quoted from Nazi propaganda more than once. He is, to put it mildly, not well-liked by a large number of people on the left, in the center, or on the right.
That's why it's surprising he put himself in the middle of protests taking place on Inauguration Day in Washington DC. No one there was more likely to hate Spencer than the black bloc anarchists in the crowd.
Black bloc protesters conceal their identities and make it a point to be destructive when participating in any kind of civil unrest. Apparently, as seen in the video above, Spencer's attacker was part of the black bloc faction on the DC streets—given the hoodie and face covering—and he was bent on destroying Spencer's jaw.
He got a solid sucker punch in, as the video shows, and Spencer went down hard. He seemed to recover well enough, but the Internet went to town with "Captain America punching Nazis" jokes about the footage.
Violence is bad, white supremacists are evil—but we admit, we could watch Captain America punching Hitler all day.