Violent, aggressive (6)
I believe the answer is:
fierce
This clue is a double definition.
'violent' is the first definition.
(I know that violent can be written as fierce)
'aggressive' is the second definition.
(I've seen this before)
(Other definitions for fierce that I've seen before include "Menacingly wild" , "Vicious" , "Menacing" , "Ferocious, savage" , "intensity" .)