Violent protester (6)
I believe the answer is:
rioter
'violent protester' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rioter that I've seen before include "Troublemaker involved in disturbing the peace" , "Disturber of the peace, looter" , "Rebel" , "He is taking part in a public affray" , "One of a crowd involved in wild disturbance" .)