Fight back at atelier resolved (9)
I believe the answer is:
Here is my best explanation:
'fight back' is the definition.
'at atelier resolved' is the subsidiary indication.
'resolved' is an anagram indicator.
'atatelier' anagrammed gives 'retaliate'.
(Other definitions for retaliate that I've seen before include "Strike back, counter", "Fight back", "Get revenge", "Make tit-for-tat attack", "Strike back, avenge", "Take revenge for a perceived wrong", "Attack in return for attack", "Get one's own back", "Give back blow for blow" and "Repay injury with similar one".)