Is getting in support to put up a fight (6)
I believe the answer is:
resist
'put up a fight' is the definition.
(I've seen this in another clue)
'is getting in support' is the wordplay.
'getting in' means one lot of letters goes inside another.
'support' becomes 'rest' (e.g. a shoulder rest is a support for shoulder).
'is' put within 'rest' is 'RESIST'.
'to' acts as a link.
(Other definitions for resist that I've seen before include "Stand firm against" , "Put up opposition to sister" , "'Withstand, fight against (6)'" , "Sister (anag)" , "Oppose, put up defence" .)