Proper contest: 50 going (3)
I believe the answer is:
due
'proper' is the definition.
(I've seen this in another clue)
'contest 50 going' is the wordplay.
'contest' becomes 'duel' (I've seen this before).
'50' becomes 'l' (Roman numeral).
'going' suggests deleting specific letters.
'duel' with 'l' taken away is 'DUE'.
(Other definitions for due that I've seen before include "Expected, scheduled" , "Scheduled to arrive" , "Unpaid or expected" , "Rightful" , "Appropriate - fee - now owing" .)