Claims one is a fighter (8)
I believe the answer is:
contends
'claims' is the definition.
('contend' can be a synonym of 'claim')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for contends that I've seen before include "Strives against another" , "Vies" , "Fights or argues" , "Strives; maintains" , "Maintains or asserts" .)