A new supporter turning up as a heavenly messenger (5)
I believe the answer is:
angel
'a heavenly messenger' is the definition.
(I've seen this in another clue)
'a new supporter turning up' is the wordplay.
'new' becomes 'n' (abbreviation as in New Testament NT).
'supporter' becomes 'leg' (eg support for a table).
'turning up' shows that the letters should be reversed in order.
'leg' backwards is 'gel'.
'a'+'n'+'gel'='ANGEL'
'as' is the link.
(Other definitions for angel that I've seen before include "Heavenely messenger" , "Heavenly being - 21 (anag)" , "Obliging person" , "Divine messenger" , "somewhere in Islington" .)