Quickly and without warning (8)
I believe the answer is:
abruptly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">quickly and without 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 abruptly that I've seen before include "brusque manner" , "In curt or disconnected manner" , "Quickly and without warning" , "In a sudden way" , "Suddenly and unexpectedly" .)