Back in the not so great 60s and 70s, it wasn't that uncommon for the so-called 'peaceniks' to lob rocks or bricks at the police, even if they weren't arresting anyone.
Ah yes, terrible 1960s memories.....Hippie threats to put LSD in the water supply....Yippies pouring blood over windows and desks of ROTC offices.....anarcists throwing bags of urine/feces at anyone in a uniform.
I remember the peaceniks well. They were as violent as anyone else (and more violent than most) toward the 'pigs' as they liked to call our police forces.