Winning suitable post (7)
I believe the answer is:
upright
'post' is the definition.
(vertical post)
'winning suitable' is the wordplay.
'winning' becomes 'up' (eg being up at half time in football).
'suitable' becomes 'right' (synonyms).
'up'+'right'='UPRIGHT'
(Other definitions for upright that I've seen before include "Type of piano" , "extremely reliable?" , "Standing straight up" , "Vertically honourable?" , "Vertical post in rugby goal - strictly honourable" .)