He daren't upset a supporter (8)
I believe the answer is:
adherent
'a supporter' is the definition.
(I've seen this before)
'he daren't upset' is the wordplay.
'upset' indicates anagramming the letters.
'he'+'darent'='hedarent'
'hedarent' with letters rearranged gives 'ADHERENT'.
(Other definitions for adherent that I've seen before include "Follower, partisan" , "One believes in and helps spread the doctrine of another" , "Freak" , "supporter of party" , "Devotee" .)