Some disrespect etc offended backing musicians (5)
I believe the answer is:
octet
'musicians' is the definition.
(I've seen this before)
'some disrespect etc offended backing' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'backing' says the letters should be written in reverse.
'tetco' is hidden within 'disrespect etc offended'.
'tetco' backwards is 'OCTET'.
(Other definitions for octet that I've seen before include "Lines of verse" , "Piece for eight players" , "Group that plays" , "Mendelssohn or Schubert piece" , "Musical composition for eight performers" .)