District record broken by bit of a swimmer, a competitor as yet unbeaten? (7-8)

'swimmer a competitor as yet unbeaten?' is the definition.
I can't tell whether this definition defines the answer.

'district record broken by bit of a' is the wordplay.
I cannot quite see how this works, but
'district' could be 'quarter' (quarter is a kind of district) and 'quarter' is found within the answer.
'record' could be 'list' (list is a type of record) and 'list' is located in the answer.
'bit' could be 'i' (resembles 1, a binary digit or bit) and 'i' is found within the answer.
'a' is within the answer.
This explanation may well be incorrect...

Can you help me to learn more?