A nut winning (5)
I believe the answer is:
ahead
'winning' is the definition.
(both can mean in the lead)
'a nut' is the wordplay.
'nut' becomes 'head' (nut can mean one's head).
'a'+'head'='AHEAD'
(Other definitions for ahead that I've seen before include "likely to win?" , "What's down the road" , "advanced" , "Winning" , "Forwards" .)