Old composer upset scruffy heavy metal fan (5)
I believe the answer is:
grebo
'heavy metal fan' is the definition.
(I've seen this before)
'old composer upset' is the wordplay.
'old' becomes 'o' (abbreviation).
'composer' becomes 'berg' (20th Century Austrian composer).
'upset' says the letters should be written backwards.
'o'+'berg'='oberg'
'oberg' written backwards gives 'GREBO'.
'scruffy' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for grebo that I've seen before include "devotee of heavy metal" , "Heavy metal fan" , "Long-haired youth" .)