Performer starting to sparkle in fancy attire (7)
I believe the answer is:
artiste
'performer' is the definition.
(artiste is a kind of performer)
'starting to sparkle in fancy attire' is the wordplay.
'starting to' says to take the initial letters.
'in' indicates putting letters inside.
'fancy' is an anagram indicator.
The first letter of 'sparkle' is 's'.
'attire' anagrammed gives 'artite'.
's' put into 'artite' is 'ARTISTE'.
(Other definitions for artiste that I've seen before include "nightclub entertainer?" , "Performers" , "Tears it (anag.)" , "Player" , "Attires like entertainer" .)