Excessive action (8)
I believe the answer is:
overkill
'excessive action' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for overkill that I've seen before include "much more than required" , "Surplus of capacity for task - sounds lethal" , "Excessive effort for task - sounds deadly" , "Action far more drastic than necessary" , "Excessive action, armament" .)