Winning spin, a boost (6)
I believe the answer is:
upturn
'a boost' is the definition.
(thesaurus)
'winning spin' is the wordplay.
'winning' becomes 'up' (I've seen this in other clues).
'spin' becomes 'turn' (I've seen this before**).
'up'+'turn'='UPTURN'
(Other definitions for upturn that I've seen before include "Improvement, in business say" , "Improving trend" , "Improvement, better trend in business" , "Rise" , "Improvement in business activity" .)