Police are appealing for witnesses to an assault outside the Turks Head pub in Aswell Street on Saturday evening (February 3).
The assault took place at around 11.40pm, and a man was knocked unconscious. He was taken to Louth County Hospital for treatment.
Another man in his 20s was arrested, and has been released under investigation.
Lincolnshire Police are appealing for witnesses. If you have information, call 101 and quote incident number 483 of February 3.
Anonymous reporting is also available through Crimestoppers on 0800 555 111, or via www.crimestoppers-uk.org/