Boasted that credit was due? (6)
I believe the answer is:
crowed
'boasted' is the definition.
(crowing is a kind of boasting)
'credit was due?' is the wordplay.
I cannot really understand how this works, but
'credit' could be 'cr' (abbreviation) and 'cr' is found within the answer.
'due?' could be 'owed' (synonyms) and 'owed' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'that' acts as a link.
Can you help me to learn more?
(Other definitions for crowed that I've seen before include "Boasted" , "was triumphant" .)