Violent farm animal on quiet worker (7)
I believe the answer is:
rampant
'violent' is the definition.
(thesaurus)
'farm animal on quiet worker' is the wordplay.
'farm animal' becomes 'ram' (male sheep).
'on' is a charade indicator (letters next to each other).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'worker' becomes 'ant' (worker is a type of ant).
'ram'+'p'+'ant'='RAMPANT'
(Other definitions for rampant that I've seen before include "Mantrap (anag) - unrestrained" , "Showing unchecked growth" , "Uncontrolled" , "Flourishing excessively as disease may be" , "Spreading unchecked" .)