They're fighting about the still to be resolved subscriptions (9)
I believe the answer is:
duellists
'they're fighting' is the definition.
The definition suggests an adverb but the answer is not.
'about the still to be resolved subscriptions' is the wordplay.
'about' indicates putting letters inside.
'to be resolved' indicates an anagram.
'subscriptions' becomes 'dues' (I can't explain this - if you can you should give a lot more credence to this answer).
'still' anagrammed gives 'llist'.
'llist' inserted within 'dues' is 'DUELLISTS'.
Can you help me to learn more?
(Another definition for duellists that I've seen is " Jousters".)