Disgusting agent turned gun on worker (9)
I believe the answer is:
repugnant
'disgusting' is the definition.
(I've seen this before)
'agent turned gun on worker' is the wordplay.
'agent' becomes 'rep' (short for representative).
'turned' is an anagram indicator.
'on' is a charade indicator (letters next to each other).
'worker' becomes 'ant' (worker is a type of ant).
'gun' with letters rearranged gives 'ugn'.
'rep'+'ugn'+'ant'='REPUGNANT'
(Other definitions for repugnant that I've seen before include "Abhorrent" , "Disgusting" , "Offensive to the mind" , "revolting" , "Very unwelcome" .)