Battles unruly sisters (7)
I believe the answer is:
resists
'battles' is the definition.
'unruly sisters' is the wordplay.
'unruly' indicates an anagram.
'sisters' with letters rearranged gives 'RESISTS'.
(Other definitions for resists that I've seen before include "Struggles against" , "Tries to stop" , "Sisters (anag.)" , "Opposes, puts up fight" , "Defies" .)