Fight back at atelier resolved (9)
I believe the answer is:
retaliate
'fight back' is the definition.
(I've seen this before)
'at atelier resolved' is the wordplay.
'resolved' indicates anagramming the letters.
'at'+'atelier'='atatelier'
'atatelier' is an anagram of 'RETALIATE'.
(Other definitions for retaliate that I've seen before include "Repay injury with similar one" , "Strike back, counter" , "Attack in return for attack" , "Return like for like" , "Exact retribution" .)