Physical aggression (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
violence
'physical aggression' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for violence that I've seen before include "Act of aggression, physical force" , "Destructive force" , "Btutality" , "Force, injury" , "Aggro" .)