Fence non-British fighter (4)
I believe the answer is:
oxer
'fence' is the definition.
(I've seen this before)
'non-british fighter' is the wordplay.
'non' is a deletion indicator.
'british' becomes 'b' (abbreviation e.g. in BBC).
'fighter' becomes 'boxer' (boxers fight each other).
'boxer' with 'b' taken out is 'OXER'.
(Other definitions for oxer that I've seen before include "Fence" , "obstacle" , "fencing" .)