Backlash concerning section of the orchestra (12)
I believe the answer is:
repercussion
'backlash' is the definition.
(I know that backlash can be written as repercussion)
'concerning section of the orchestra' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'section of the orchestra' becomes 'percussion' (I've seen this before).
're'+'percussion'='REPERCUSSION'
(Other definitions for repercussion that I've seen before include "Recoil; reverberation" , "Indirect effect; echo" , "Impact" , "Unintended consequence" , "Backlash" .)