Rapid rise (7)
I believe the answer is:
upsurge
'rapid rise' is the definition.
(I've seen this before)
This is all the clue.
(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" .)