Rapid rise (7)
I believe the answer is:
upsurge
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rapid rise</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 upsurge that I've seen before include "A sudden rise, as in business" , "Sudden large increase" , "Hike" , "Sudden forceful flow from below" , "A sudden rise as in fortunes" .)