Over-ready to shoot (7-5)
I believe the answer is:
trigger-happy
'over-ready to shoot' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for trigger-happy that I've seen before include "inclined to recklessness" , "Over-ready to shoot" , "Quick to use a gun" , "Over-enthusiastic with a gun" , "Irresponsible with firearms" .)