Randomly chosen composer – this one? (10)
I believe the answer is:
schoenberg
'this one?' is the definition.
The definition suggests a singular noun which matches the answer.
'randomly chosen composer' is the wordplay.
'randomly' indicates an anagram (I've seen 'roaming randomly' mean this).
'composer' becomes 'berg' (20th Century Austrian composer).
'chosen' with letters rearranged gives 'schoen'.
'schoen'+'berg'='SCHOENBERG'
(Other definitions for schoenberg that I've seen before include "Austrian scorer" , "Arnold --, Austrian-born composer" .)