Police are now appealing for witnesses to the assault, which happened in the toilets of the Crafty Scholar pub in Church Street on Thursday December 22 just after midnight.
The boy, from Lancaster, had gone to the toilets where a man was acting aggressively.
The man, who was wearing a grey tracksuit, then started shouting at the boy’s friend, and after the boy told him they didn’t want any trouble, he was punched in the face causing concussion and a cut that required stitches.
PC 2320 James Buddo from Lancaster Police said: “The victim was simply trying to innocently diffuse a situation when he was punched to the face during what should have been Christmas celebrations. Instead he ended up needing hospital treatment.
“We need anyone who may have been in the toilets at the time, or anyone with information that could help to come forward.”
If you have any information, please call us on 101 quoting incident reference 199 of December 22nd. Alternatively Crimestoppers can be contacted anonymously on 0800 555111 or online at www.crimestoppers-uk.org.