Fencer's warning (2,5)
I believe the answer is:
en garde
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fencer's warning</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 en garde that I've seen before include "warning of attack" , "Fencer's warning cry" , "Prepare to fence!" , "Angered with opening position in fencing - be alert. (2,5)" , "Get ready to fence" .)