The ruling standard is Brandenburg v. Ohio, which draws the line at incitement to "imminent lawless action." Which is to say, you have to be rallying people to start a riot right now. Doing something that is merely provocative, such as marching a neo-Nazi parade through a neighborhood of Holocaust survivors, is protected First Amendment speech.

Literally shouting fire in a crowded theater in an attempt to cause a panic and perhaps kill people, would not be protected speech, but pretty much anything less would be protected speech.