Solo perhaps conducted after upsetting composer (6)
I believe the answer is:
handel
'composer' is the definition.
(George Frideric Handel)
'solo perhaps conducted after upsetting' is the wordplay.
'solo perhaps' becomes 'han' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'conducted' becomes 'led' ('lead' can be a synonym of 'conduct').
'after upsetting' says the letters should be written backwards (in a down clue, letters go up).
'led' back-to-front is 'del'.
'han'+'del'='HANDEL'
Can you help me to learn more?
(Other definitions for handel that I've seen before include "German composer, George Frederick (1685-1759)" , "music-maker" , "German scorer" , "German-born composer to the ` `Messiah' '" , "German composer of Messiah" .)