Bet about name for composer (6)
I believe the answer is:
wagner
'for composer' is the definition.
(Richard Wagner)
'bet about name' is the wordplay.
'bet' becomes 'wager' (synonyms).
'about' is an insertion indicator.
'name' becomes 'n' (common abbreviation e.g. on forms).
'wager' placed around 'n' is 'WAGNER'.
(Other definitions for wagner that I've seen before include "We rang up the composer" , "German opera composer" , "Richard . . . . . . composer of 'The Flying Dutchman' and 'Lohengrin'" , "German composer of The Flying Dutchman" , "German composer of The Ring Cycle" .)