Runs riot (8)
I believe the answer is:
rampages
'runs riot' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rampages that I've seen before include "Moves through a place in a violent and uncontrollable way" , "Violent and destructive behaviours" , "Runs riot" , "Violent disorders" , "Rushes around wildly" .)