A 54-year-old dog walker was punched in the face following an argument with another dog walker.
The victim was walking with her small white dog on Northampton Racecourse, about 90 meteres from the White Elephant Pub, at about 5pm on Sunday.
She was approached by a woman with a grey Staffordshire bull terrier and the pair argued about a fight between their dogs the previous week.
The woman with the bull terrier then punched the victim in the face, causing her to fall to the floor.
She suffered a bruise to the left side of her face.
The offender is descried as Asian, about 20-years-old and slim with straight, black, shoulder-length hair and a pointy nose.
Officers are appealing for witnesses and in particular would like to speak with two men who helped the victim.
Anyone with any information can call Northamptonshire Police on 101. Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111.