Person at a symphony clutching pieces of music (7)
I believe the answer is:
sonatas
'pieces of music' is the definition.
'person at a symphony clutching' is the wordplay.
'clutching' indicates the answer is hidden within the clue.
'SONATAS' is hidden in the letters of 'person at a symphony'.
(Other definitions for sonatas that I've seen before include "musical items" , "10 [COMPOSITION]s" , "Piano pieces" , "Works" , "Classical pieces" .)