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