Outcome of winning attempt (6)
I believe the answer is:
upshot
'outcome' is the definition.
(I know that outcome can be written as upshot)
'winning attempt' is the wordplay.
'winning' becomes 'up' (eg being up at half time in football).
'attempt' becomes 'shot' (shot is a kind of attempt).
'up'+'shot'='UPSHOT'
'of' acts as a link.
(Other definitions for upshot that I've seen before include "One killed the albatross" , "skier" , "anti-aircraft fire?" , "increased exposure" , "Outcome of vertical discharge?" .)