Rifleman (6)
I believe the answer is:
sniper
'rifleman' is the definition.
(I have seen 'Hidden rifleman ' mean 'sniper' so perhaps 'rifleman' could also mean 'sniper')
This is all the clue.
(Other definitions for sniper that I've seen before include "Concealed gunner" , "Hidden gunman" , "One trained to shoot" , "one who takes pot from a safe place" , "One shooting from concealed position" .)