Left after outstanding contest (4)
I believe the answer is:
duel
'contest' is the definition.
(fight between two people)
'left after outstanding' is the wordplay.
'left' becomes 'L' (common abbreviation).
'after' is a charade indicator (letters next to each other).
'outstanding' becomes 'due' (I've seen this before).
'l' after 'due' is 'DUEL'.
(Other definitions for duel that I've seen before include "Affair of honour (between two men)" , "Contest between two people, perhaps with weapons" , "Fight between two people over an affair of honour" , "honourable affair" , "shoot-out?" .)