Justifies fighting and a lot of abuse (8)
I believe the answer is:
warrants
'justifies' is the definition.
('warrant' can be a synonym of 'justify')
'fighting and a lot of abuse' is the wordplay.
'fighting' becomes 'war'.
'and' is a charade indicator (letters next to each other).
'a lot of abuse' becomes 'rants' (I can't explain this - if you can you should believe this answer much more).
'war'+'rants'='WARRANTS'
Can you help me to learn more?
(Other definitions for warrants that I've seen before include "Rats warn about documents authorising arrest or search" , "Justifies" , "Calls for - authorisations" , "Written authorisations as for arrest" , "'Written legal authorisations, to make arrests say (8)'" .)