Drummer in boring outfit (5)
I believe the answer is:
ringo
'drummer' is the definition.
(Ringo Starr)
'in boring outfit' is the wordplay.
'in' indicates the answer is hidden within the clue.
'RINGO' can be found hidden inside 'boring outfit'.
(Other definitions for ringo that I've seen before include "Starr drummer" , "Member of group" , "One of The Beatles" , "Beatle Starr" , "The drumming Beatle" .)