Snowball (8)
I believe the answer is:
escalate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">snowball</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 escalate that I've seen before include "Cause to increase, say dispute (8)." , "Increase in intensity or extent, like trouble brewing" , "Tease Cal badly and mount up" , "Rapidly increase in intensity" , "mushroom" .)