So, who are are the Nazis? Does antifa have a show trial before executing sentences? Or do they just go around punching people they think are Nazis? Antifa and their ilk are just calling everyone Nazis, so is everyone they don't like getting punched?

Antifa is a violent organization that has labeled free speech as violent. Unfortunately, for this wing of international socialism, there is no legal precedent in the USA that allows for actual violence as self defense (LOL) against nonviolent speech. There is no yelling "Fire!" in a crowded auditorium exception here, and even if there was antifa is not an accepted enforcer of that law.