New rag improvised by a composer (6)
I believe the answer is:
wagner
'a composer' is the definition.
(Wagner is an example)
'new rag improvised' is the wordplay.
'improvised' indicates an anagram (I've seen this in other clues).
'new'+'rag'='newrag'
'newrag' anagrammed gives 'WAGNER'.
'by' acts as a link.
(Other definitions for wagner that I've seen before include "Richard . . . . . . composer of 'The Flying Dutchman' and 'Lohengrin'" , "Composer of ''The Flying Dutchman'' etc" , "Noted German" , "We rang up the composer" , "German composer of The Ring Cycle" .)