Pole in fight (4)
I believe the answer is:
spar
I believe this is a double definition.
'pole' is the first definition.
(spar is a kind of pole)
'fight' is the second definition.
(sparring is a kind of fighting)
'in' acts as a link.
(Other definitions for spar that I've seen before include "Mast - boom - gaff" , "Crystal - box" , "Pole-shaped part of the rigging" , "Yard" , "Pole used to support sails or rigging" .)