There is more here: https://www.cbsnews.com/philadelphia/news/quakertown-pa-ice-protest-students-arrests/

"Police claim some of the students threw snowballs, kicked cars and damaged property as the protest reached East Broad Street. They claim a side mirror from a car was torn off."

Still no reason to assault anyone, let alone teenagers.

"Students said a man in plain clothes appeared to charge into the crowd and began throwing punches. They said they did not initially realize he was a police officer."

I'll believer the kids over the cops.