Fellow among celebrities is a top performer (8)
I believe the answer is:
finalist
'a top performer' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'fellow among celebrities' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'among' becomes 'in' (I've seen this in other clues).
'celebrities' becomes 'alist' (A-list).
'f'+'in'+'alist'='FINALIST'
'is' is the link.
Can you help me to learn more?
(Other definitions for finalist that I've seen before include "Competitor who has beaten all except one" , "One reaching last match" , "So far unbeaten competitor" , "Competitor who reaches the last stage" , "Sportsman who gets into the last round" .)