Proper contest shortened (3)
I believe the answer is:
due
'proper' is the definition.
(what is due is what is proper or appropriate)
'contest shortened' is the wordplay.
'contest' becomes 'duel' (fight between two people).
'shortened' means to remove the last letter.
'duel' with its final letter taken off is 'DUE'.
(Other definitions for due that I've seen before include "Payable; deserved" , "Ripe for payment or arrival" , "Expected at any moment" , "Expected; appropriate" , "Proper, appropriate" .)