Outside clubs, the roars upset group of musicians (9)
I believe the answer is:
orchestra
'group of musicians' is the definition.
(I've seen this before)
'outside clubs the roars upset' is the wordplay.
'outside' indicates putting letters inside.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'upset' indicates anagramming the letters.
'the'+'roars'='theroars'
'theroars' is an anagram of 'orhestra'.
'c' put inside 'orhestra' is 'ORCHESTRA'.
(Other definitions for orchestra that I've seen before include "Group of musical instrumentalists" , "LSO, for example" , "Large group of musicians" , "many players" , "Assembly of musicians as in pit" .)