Victory by good side (4)
I believe the answer is:
wing
'side' is the definition.
(I've seen this in other clues)
'victory by good' is the wordplay.
'victory' becomes 'win' (I've seen this before**).
'by' means one lot of letters go next to another.
'good' becomes 'g' (abbreviation).
'win'+'g'='WING'
(Other definitions for wing that I've seen before include "Appendage aiding flight" , "Part of car over wheel" , "attacker on side" , "Chicken portion" , "Faction; annexe" .)