A 22-year-old man lost a chunk of his ear and had to be treated at hospital after a fight on a cycle path in Hull.
The man was walking along the track between Bude Road and Wawne Road roundabout at around 2345 BST on Friday.
He passed a man with a dog, at which point the animal allegedly bit him.
He confronted the owner, which led to an argument between the two men. Police said a "scuffle" ensued and he lost some of his ear.
The victim struggled free and ran off from the scene.
He attended Hull Royal Infirmary for treatment to the wound.
The suspect is described as white, between 35 and 40 years old, 5ft 11ins or 6ft tall and of heavy build.
He had a shaven head, stubble on his face and spoke with a local accent.
He was wearing a red England T-shirt, black and white Adidas tracksuit bottoms, and black and white Adidas Samba trainers.
He was walking a small white and ginger coloured spaniel dog.
Police are appealing for witnesses.