There are other news reports that police were slow to respond.
Hindsight is always 20-20, but I hope police departments in other cities where white nationalists hold demonstrations are more quick to respond to any fights that break out.
Police also need to create better buffers between demonstrators and counter-demonstrators.
Finally, regardless of what people think of white nationalists, they have a right to demonstrate peacefully. Period.
I think counter-demonstrators literally turning their backs on them (legal, non-violent, symbolic) as they pass would be more effective than punching them in the nose (not legal, violent).