Outshine in winning leg (7)
I believe the answer is:
upstage
'outshine' is the definition.
(upstaging is a kind of outshining)
'winning leg' is the wordplay.
'winning' becomes 'up' (I've seen this in other clues).
'leg' becomes 'stage' ('stage' can be a synonym of 'leg').
'up'+'stage'='UPSTAGE'
'in' acts as a link.
(Other definitions for upstage that I've seen before include "dwarf?" , "Try to attract attention" , "moved away from the audience" , "Divert attention from another as actor may" , "Divert attention from someone towards yourself" .)