Rock group backed number selected to play new recording? (5)
I believe the answer is:
remix
'new recording?' is the definition.
'rock group backed number selected to play' is the wordplay.
'rock group' becomes 'rem' (REM are a US rock band).
'backed' shows that the letters should be reversed in order.
'number selected to play' becomes 'xi' (an XI or eleven is a football team).
'xi' written backwards gives 'ix'.
'rem'+'ix'='REMIX'
(Other definitions for remix that I've seen before include "Make a new version of a recording" , "New blend (recording, recipe, etc)" , "Music produced by electronic alteration of tracks" , "Modified musical recording" , "Revised pop song" .)