Fights against spoilt sisters (7)
I believe the answer is:
resists
'fights against' is the definition.
(I've seen this in another clue)
'spoilt sisters' is the wordplay.
'spoilt' is an anagram indicator.
'sisters' anagrammed gives 'RESISTS'.
(Other definitions for resists that I've seen before include "Tries to stop" , "Is hostile to" , "Fights back" , "Defies" , "Stands up to, withstands" .)