A case for fighting (6)
I believe the answer is:
action
This clue is a double definition.
'a case' is the first definition.
('action' can be a synonym of 'case')
'fighting' is the second definition.
(thesaurus)
'for' is the link.
(Other definitions for action that I've seen before include "Fighting - lawsuit" , "The mechanism of, say, a watch" , "Lawsuit; thing done" , "Watch operating mechanism" , "Operation; engagement" .)