Supporter he daren't cast out (8)
I believe the answer is:
adherent
'supporter' is the definition.
(I've seen this before)
'he daren't cast out' is the wordplay.
'cast' indicates an anagram (letters are dispersed or cast around).
'out' is an insertion indicator.
'darent' anagrammed gives 'adrent'.
'he' going into 'adrent' is 'ADHERENT'.
(Other definitions for adherent that I've seen before include "Freak" , "supporter of party" , "One believes in and helps spread the doctrine of another" , "Loyal follower - sticks close" , "Supporter, fan" .)