Piece from Mozart, he's piano player (8)
I believe the answer is:
thespian
'player' is the definition.
('thespian' can be a synonym of 'player')
'piece from mozart he's piano' is the wordplay.
'piece' indicates a hidden word.
'THESPIAN' is hidden within 'from mozart hes piano'.
(Other definitions for thespian that I've seen before include "Dramatic actor" , "Player" , "Stage actor" , "stage performer" , "Tragic actor" .)