Proper learner in fight (4)
I believe the answer is:
duel
'fight' is the definition.
(duel is a kind of fight)
'proper learner' is the wordplay.
'proper' becomes 'due' (I've seen this before).
'learner' becomes 'l'.
'due'+'l'='DUEL'
'in' is the link.
(Other definitions for duel that I've seen before include "Contest to settle point of honour" , "Contest between two with deadly weapons" , "Contest between two people, perhaps with weapons" , "honourable affair" , "Fight over a point of honour" .)