Hidden marksman (6)
I believe the answer is:
sniper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hidden marksman</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sniper that I've seen before include "Good shot" , "Rifleman firing from concealed location" , "Hidden marksman" , "One trained to shoot" , "He fires shots from hidingplace" .)