Fine due over brawl (4)
I believe the answer is:
feud
'brawl' is the definition.
(thesaurus)
'fine due over' is the wordplay.
'fine' becomes 'f' (abbreviation).
'over' says the letters should be written in reverse.
'due' back-to-front is 'eud'.
'f'+'eud'='FEUD'
(Other definitions for feud that I've seen before include "Bitter quarrel between two parties" , "State of prolonged mutual hostility" , "Sustained enmity" , "Prolonged fight between families, very Sicilian" , "Private war" .)