Bit of Birtwistle embraced by rock nonconformist (5)
I believe the answer is:
rebel
'nonconformist' is the definition.
(I know that rebel is a type of nonconformist)
'bit of birtwistle embraced by rock' is the wordplay.
'bit of' suggests taking the first letters.
'embraced by' means one lot of letters goes inside another.
'rock' becomes 'reel' (reel can mean to rock around).
The initial letter of 'birtwistle' is 'b'.
'b' put inside 'reel' is 'REBEL'.
(Other definitions for rebel that I've seen before include "Oppose authority" , "One resisting authority" , "Freedom fighter?" , "Anti-establishment figure" , "One who won't comply" .)