So-so ban over the instrument (7)
I believe the answer is:
bassoon
'so-so ban over the instrument' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bassoon that I've seen before include "Hollow instrument" , "So-so ban on the instruments" , "Instrument - no ASBOs (anag)" , "Instrument heard by Wedding-Guest" , "No, a boss would be a musical instrument" .)