Feud great with NUM in turmoil (8)
I believe the answer is:
'feud' is the definition.
'great with num in turmoil' is the wordplay.
'with' is a charade indicator (letters next to each other).
'in turmoil' indicates anagramming the letters (I've seen this in other clues).
'great' after 'num' is 'numgreat'.
'numgreat' anagrammed gives 'ARGUMENT'.
(Other definitions for argument that I've seen before include "that may be constructed on premises" , "Heated disagreement" , "Discussion - line of proof" , "Quarrel, row" , "Clash of opinions" .)