Unsparing (8)
I believe the answer is:
ruthless
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unsparing</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 ruthless that I've seen before include "Brutal" , "hard" , "Showing no mercy" , "Showing no compassion" , "Having no mercy like hustlers" .)