Head off to hire a supporter (8)
I believe the answer is:
adherent
'a supporter' is the definition.
(I've seen this before)
'head off to hire' is the wordplay.
'off' is an anagram indicator.
'to hire' becomes 'rent' ('rent' can be a synonym of 'hire').
'head' with letters rearranged gives 'adhe'.
'adhe'+'rent'='ADHERENT'
(Other definitions for adherent that I've seen before include "sticker" , "Devotee" , "lover" , "Person supporting" , "One supports" .)