A woman was kicked repeatedly and damaged a tendon while she was walking her dog on a footpath in Northampton.
The incident happened between Greatmeadow and Blackthorn Road on Christmas day between noon and 12.30pm, Northamptonshire Police today said.
The victim, who was with a relative, was approached by a man and woman who were also walking their dog.
The woman pushed the victim, causing her to fall, and then kicked her repeatedly.
She sustained suspected fractures to her ribs, a damaged tendon to her hand and bruising.
A spokeswoman for the force said: "The offender is described as white, aged about 20, 5ft to 5ft 2in, with a slim build, a pale complexion and collar to shoulder length dark hair.
"She was wearing a black leather jacket with a circular motif on the back, and black boots."
Witnesses to the incident, or anyone with information, are asked to contact Northamptonshire Police on 101. Alternatively, they can call Crimestoppers anonymously on 0800 555111.