Attack, as a castle (5)
I believe the answer is:
storm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">attack as a castle</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for storm that I've seen before include "violent assault" , "rave" , "SECOND PART OF 1 DOWN" , "Furore" , "commotion" .)