Composer from Berlin is sorely upset (7)
I believe the answer is:
rossini
'composer' is the definition.
(Italian composer Gioachino Rossini)
'from berlin is sorely upset' is the wordplay.
'from' indicates a hidden word.
'upset' says the letters should be written in reverse.
'inissor' can be found hidden inside 'berlin is sorely'.
'inissor' reversed gives 'ROSSINI'.
(Other definitions for rossini that I've seen before include "Barber of Seville writer" , "Composer born 29 Feb 1792" , "Italian scorer" , "Staff writer" , "Gioacchino ---, It. composer" .)