A man in his 20s was assaulted and left with head injuries near to the Brayford in Lincoln.
Attackers fled the scene, but the victim was helped by a number of people on Brayford Wharf East on the junction with Wigford Way.
The attack happened between 3am and 3.45am on Wednesday, December 13.
Lincolnshire Police area appealing for help from anyone who witnessed the incident and hasn’t already spoken with officers.
They said vast numbers of people helped at the scene.
A spokesperson from the force said: “If you did see anything, please ring 101 and ask to be put through to Lincoln CID, stating that this is for the attention of PC 399 Lawrence.”