Sudden rush (8)
I believe the answer is:
stampede
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sudden rush</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 stampede that I've seen before include "Rapid flight" , "herd scatter wildly" , "Panic-stricken charge of cattle" , "Headlong rush of a group in panic" , "Deems apt to have flight of cattle" .)