Violent reaction (5)
I believe the answer is:
storm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">violent reaction</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 storm that I've seen before include "rave" , "rage" , "Violent outburst" , "Trouble" , "Wind force 10 on Beaufort scale" .)