Crushing defeat (4)
I believe the answer is:
rout
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">crushing defeat</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 rout that I've seen before include "Inflict heavy defeat on" , "Whitewash" , "Rowdy mob" , "Total defeat in battle" , "Drubbing" .)