The incident happened at shortly before 10pm on Saturday, April 1 when the 36-year-old victim was walking with two friends along Church Street towards the Stonewell Tavern.
Police say that as the friends passed a large group of youths a small sign and traffic cone was thrown at them. One of the youths from the group then approached the victim from behind and punched him to the back of the head and then to the face. The victim suffered a swollen and bloody nose as a result of the attack.
The offender is described by officers as aged 13 to 14 years old and was wearing a grey hooded top with “Superdry” written on the front in white. He was on a black mountain bike.
PC Mark Howson of Lancaster Police said: “This was a random and unprovoked attack on the victim who was simply walking past the group of youths with his friends. If anyone witnessed what happened and has not yet spoken to us I would urge them to get in touch.
“I am also keen to hear from anyone who may have any mobile phone or CCTV footage of the incident.”
Anyone with information can contact police on 101 quoting log 1601 of April 1.
Alternatively independent charity Crimestoppers can be contacted anonymously on 0800 555 111 or online at Crimestoppers-uk.org.