Did back hurt, day after boy carries piano? (9)
I believe the answer is:
sponsored
'did back' is the definition.
(back can mean to sponsor)
'hurt day after boy carries piano?' is the wordplay.
I cannot quite see how this works, but
'hurt' could be 'sore' (I've seen this in another clue) and 'sore' is located in the answer.
'day' could be 'd' (abbreviation for day) and 'd' is present in the answer.
'piano?' could be 'p' (musical abbreviation) and 'p' is located in the answer.
'boy' could be 'son' (synonyms) and 'son' is found within the remaining letters.
No letters remain.
This explanation may well be incorrect...
(Other definitions for sponsored that I've seen before include "(Of event) supported financially" , "With backing" .)