Piece of music which Swiss hero managed not to broadcast (9)
I believe the answer is:
bagatelle
'piece of music' is the definition.
(I've seen this before)
'swiss hero managed not to broadcast' is the wordplay.
I cannot quite see how this works, but
'hero' could be 'tell' (I have seen 'Swiss hero ' mean 'tell' so perhaps 'hero' could also mean 'tell') and 'tell' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'which' is the link.
(Other definitions for bagatelle that I've seen before include "trifling amount" , "Pinball game - something of little value" , "Something trivial" , "Trifle - game with pins and balls" , "Trinket - game played on a board with balls" .)