Ladies and gents engage a new supporter to defend a barman (6,7)
I believe the answer is:
'barman' is the definition.
(composer - someone who wrote bars of music)
'ladies and gents engage a new supporter to defend a' is the wordplay.
I cannot really see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'a' could be 'an' and 'an' is found in the answer.
This explanation may well be incorrect...