Anti-aircraft fire (4)
I believe the answer is:
flak
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">anti-aircraft fire</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 flak that I've seen before include "Brickbats" , "that can bring down a plane" , "Unfriendly criticism" , "Criticism (colloq.)" , "heated disagreement" .)