Knock unconscious (4)
I believe the answer is:
stun
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">knock unconscious</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 stun that I've seen before include "Numb with nuts" , "Confuse" , "Astound; render senseless" , "Daze, render semi-conscious" , "Take aback" .)