A man is claimed to have been verbally abusive to members of the public on Queen Street on July 20 before punching a person who then fell to the ground.
They hit their head and sustained a head injury.
Investigators are asking anyone who has information about the incident to get in touch.
A police spokesman said: “We believe the man pictured can help us with our enquiries.”
If you think you can help, contact DC Richard Morley by [email protected] quoting the number 24000431441.
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Do you recognise this man who may be able to help police? Photo: Lincs police