When is Assault okay?

The Left: Is Assault okay if they don't like the person? Attack on Alt-Right Leader Has Internet Asking: Is It O.K. to Punch a Nazi?

https://www.nytimes.com/2017/01/21/us/politics/richard-spencer-punched-attack.html?_r=1&utm_source=jolt&utm_medium=email&utm_campaign=Jolt%202/13/2017&utm_term=Jolt