Northern river sport? (4)
I believe the answer is:
wear
I believe this is a double definition.
'northern river' is the first definition.
(River Wear in the north east of England)
'sport?' is the second definition.
(sport can mean to wear or display on one's person)
(Other definitions for wear that I've seen before include "North-east flower" , "Dress in; erode" , "brook" , "Carry the burden" , "Be clothed in" .)