A roadie at outset called Queen’s musician (8)
I believe the answer is:
arranger
'musician' is the definition.
(someone who arranges musical performances)
'a roadie at outset called queen's' is the wordplay.
'at outset' says to take the initial letters.
'called' becomes 'rang' ('ring' can be a synonym of 'call').
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
The first letter of 'roadie' is 'r'.
'a'+'r'+'rang'+'er'='ARRANGER'
(Other definitions for arranger that I've seen before include "One adapting music for different forces" , "One doing ordaining" , "One adapting a piece of music" , "One planning" , "Rare gran (anag.)" .)