Breach metal around front of opening underneath instrument (9)
I believe the answer is:
violation
'breach' is the definition.
(I've seen this before)
'metal around front of opening underneath instrument' is the wordplay.
'metal around front of opening' becomes 'tion' (I can't explain this - if you can you should believe this answer much more).
'underneath' means one lot of letters go next to another (in a down clue, some letters go under others).
'instrument' becomes 'viola' (viola is a kind of instrument).
'tion' after 'viola' is 'VIOLATION'.
Can you help me to learn more?
(Other definitions for violation that I've seen before include "Offence" , "abuse" , "Breach" , "outrage" , "Infringement" .)