Performer of an early composition for the piano (6)
I believe the answer is:
player
'performer' is the definition.
(I know that player is a type of performer)
'an early composition for the piano' is the wordplay.
'composition' indicates anagramming the letters.
'for' says to put letters next to each other (I've seen this in other clues).
'the piano' becomes 'p' (musical abbreviation).
'early' with letters rearranged gives 'layer'.
'layer' put after 'p' is 'PLAYER'.
'of' acts as a link.
(Other definitions for player that I've seen before include "Partaker in game" , "Gamer or sportsman" , "Game's participant" , "Gambler" , "one on the wing, perhaps?" .)