Well, that’s a real problem. In this case, there is probably nothing much to do but rely on the civil courage of citizens and hope that someone will at least take down the license plate number or that maybe a critical mass will form quickly enough to detain these idiots until the police arrives. I am glad that such actions by fascists do not (yet) exist in my country (Germany). In the city where I live, even a whole bunch of sad Nazis would have no fun at all if they tried something like that. But that can be quite different elsewhere in my home country too. I wish you the best of luck and hope that you find a way to deal with these morons. Be save!
Edit: In Germany, this kind of behavior might be enough to be investigated for forming a terrorist organization - which is what is being attempted here: spreading terror. Perhaps you can collect signatures to persuade your representatives to take action.