Heavy blow with the hand (5)
I believe the answer is:
thump
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">heavy blow with the hand</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for thump that I've seen before include "Smack" , "Punch" , "clobber" , "Hit hard" , "Whack" .)