Fight is dividing the others (6)
I believe the answer is:
resist
'fight' is the definition.
(resisting is a kind of fighting)
'is dividing the others' is the wordplay.
'dividing' indicates putting letters inside.
'the others' becomes 'rest' (I've seen this in other clues**).
'is' going within 'rest' is 'RESIST'.
(Other definitions for resist that I've seen before include "Withstand or defy" , "Express opposition" , "Put up opposition, defy" , "Stand firm against" , "Endure" .)