First, let's admit the obvious: one side could be the victims, defending themselves from attacks rather than instigating them. This could be the case even if the "defenders" came armed (for self-protection, say).
Now, I'm sure not claiming that none of the counterprotesters initiated violence, though I haven't seen reputable reports to the contrary. In any case, there's another point to be made here: even if some counterprotesters were at fault for initiating violence, it wouldn't be worth discussing unless the violence initiated by each side was roughly comparable.
Finally, of course, there's a difference between the moral worth of the issues fought for. Fighting against racism is more understandable and morally forgivable than fighting for it, even if both acts of violence are wrong.