Composer is a crank, so they say (6)
I believe the answer is:
handel
'composer' is the definition.
(George Frideric Handel)
'crank so they say' is the wordplay.
'crank' becomes 'handle'.
'so they say' shows a homophone (sound like).
'handle' is a homophone of 'HANDEL'.
'is a' acts as a link.
(Other definitions for handel that I've seen before include "British composer of German birth, the 'father of the oratorio'" , "German composer, George Frederick (1685-1759)" , "Water Music composer, d. 1759" , "German scorer" , "George Frideric --, composer" .)