Rubbish ballad finally turned down (7)
I believe the answer is:
refused
'turned down' is the definition.
('refuse' can be a synonym of 'turn down')
'rubbish ballad finally' is the wordplay.
'rubbish' becomes 'refuse' (I've seen this before).
'ballad finally' becomes 'd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'refuse'+'d'='REFUSED'
Can you help me to learn more?
(Other definitions for refused that I've seen before include "Not accepted" , "Declined, rejected" , "turned down appeal" , "Was unwilling to accept" , "Said no (7)" .)