Ann’s chum became a famous composer (8)
I believe the answer is:
'a famous composer' is the definition.
'schumann' can be an answer for 'composer' (I've seen this before). I am unsure of the 'a famous' bit.
'ann's chum became' is the wordplay.
'became' indicates anagramming the letters (I've seen 'become' mean this).
'annschum' anagrammed gives 'SCHUMANN'.
Can you help me to learn more?
(Other definitions for schumann that I've seen before include "Robert -, nineteenth century German composer" , "German composer, 1810-56" , "Robert --, German romantic composer" , "German barman" , "Nan, chums go for this composer" .)