Supporter heard ten out (8)
I believe the answer is:
adherent
'supporter' is the definition.
(I've seen this before)
'heard ten out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'heard'+'ten'='heardten'
'heardten' is an anagram of 'ADHERENT'.
(Other definitions for adherent that I've seen before include "Supporter; sticking" , "One supports" , "Follower, partisan" , "Freak" , "Devotee" .)