Just by winning post (7)
I believe the answer is:
upright
'post' is the definition.
(vertical post)
'just by winning' is the wordplay.
'just' becomes 'right' (similar in meaning).
'by' says to put letters next to each other.
'winning' becomes 'up' (eg being up at half time in football).
'right' after 'up' is 'UPRIGHT'.
(Other definitions for upright that I've seen before include "Vertical like rugby goal post" , "Keyboard instrument" , "Honest like a vertical post" , "Joanna" , "Perpendicular" .)