Singer in bar punched, assailant finally arrested (5,3)

'singer' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?

'bar punched assailant finally arrested' is the wordplay.
'bar' becomes 'Mars' (chocolate bar).
'punched' becomes 'hit' (I can't explain this - if you can you should give a lot more credence to this answer).
'finally' says to take the final letters.
'arrested' means one lot of letters goes inside another (arrest can mean to hold or imprison).
The final letter of 'assailant' is 't'.
'hit' placed around 't' is 'htit'.
'mars'+'htit'='MARSH TIT'

'in' is the link.

Can you help me to learn more?