Horrible injury from fighting? Men split (9)
I believe the answer is:
abhorrent
'horrible' is the definition.
(I've seen this before)
'injury from fighting? men split' is the wordplay.
'injury from fighting?' becomes 'abh' (abbreviation for actual bodily harm).
'men' becomes 'or' (military abbreviation for Other Ranks).
'split' becomes 'rent' (synonyms).
'abh'+'or'+'rent'='ABHORRENT'
(Other definitions for abhorrent that I've seen before include "Odious, being earthborn" , "horrid" , "Ugly" , "Rob in Tehran - that's disgusting" , "Repugnant, offensive" .)