Some work penned by Chopin, say, is revolutionary for composer (9)
I believe the answer is:
pergolesi
'for composer' is the definition.
(Italian composer)
'some work penned by chopin say is revolutionary' is the wordplay.
'some work' becomes 'erg' (scientific unit of work).
'penned by' means one lot of letters goes inside another.
'chopin say' becomes 'Pole' (composer Frederic Chopin was Polish).
'revolutionary' says the letters should be written in reverse.
'is' backwards is 'si'.
'erg' placed into 'pole' is 'pergole'.
'pergole'+'si'='PERGOLESI'
(Other definitions for pergolesi that I've seen before include "One put notes together" , "Sixteenth century Italian composer of La serva padrona" , "Italian composer known for a Stabat Mater" .)