Hidden gunman (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
sniper
'hidden gunman' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sniper that I've seen before include "One who criticises" , "Military marksman" , "One shoots from a concealed place" , "Lone rifleman" , "Concealed shooter" .)