Anti-Fascism
Also, many of their followers think that this is a game, that this a joke, that they can come off the Internet and into the streets without this having very serious implications. And a lot of what antifa is doing is making it perfectly clear to them that if you really want to be a Nazi, this is a dangerous thing and you really need to think twice about throwing yourself behind a racist white supremacist movement that is preaching the death of others.
I think that a lot of very well-intentioned people don't fully understand the truth of this statement. A significant number of channers and redditors have stumbled into the alt-right by seeking out the “lulz.”
Marching shoulder-to-shoulder with white nationalists is a significantly different proposition than showing up outside the Scientology headquarters with a Guy Fawkes mask on and playing Rick Astley on a boombox, and it carries with it a whole different set of consequences.
George Ciccariello-Maher (interviewed by Matthew Green), “What Is Antifa? A Scholar Of the Movement Explains,”, KQED.