A Good Samaritan who tried to stop a dog being kicked was left with a broken jaw when the owner attacked him.
The man, who is in his twenties, was walking with his girlfriend in Hartcliffe, Bristol, at about 2.30pm on Monday when he witnessed a man kicking and choking the pet.
But when he challenged the man and asked him to stop, the offender punched him in face.
The attacker is described as white, believed to be 17-year-old, 6ft and of slim build with blond hair.
He was wearing a grey hooded tracksuit top and trousers and a grey Nike t-shirt with the slogan 'Just Do It' in large letters across the chest. The writing was a multi-coloured design with a graffiti effect.
The dog resembled a black greyhound and was quite young. It didn't have a collar on but had a piece of black rope around its neck.
The offender was in the company of another man, described as a 17-year-old, about 5ft 8ins, of a chubby build with hair which came down to his shoulders. He was wearing a grey waterproof jacket and grey tracksuit trousers.
Detective Constable Alan Smith, of Bristol CID, said: "This was an unprovoked and violent assault on a member of the public who was concerned for the welfare of a dog.
"I would like to speak to anyone who recognises the description of the man and the dog, or who may have seen them in the Fulford Road area around the time of the incident."
Anyone with information about the incident is being asked to contact Bristol CID via the 24-hour police enquiry centre, or to contact Crimestoppers anonymously on 0800 555 111
