In town, keep out of the centre of crime or sin (4)

'sin' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?

'in town keep out of the centre of crime' is the wordplay.
'in town keep' becomes 'bai' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'out of' indicates putting letters inside (some letters on the outside of others).
'the centre of' indicates the central letters.
'crime' becomes 'porno' (porno is a kind of crime).
The centre of 'porno' is 'r'.
'bai' going around 'r' is 'BARI'.

'or' acts as a link.

Can you help me to learn more?