A 34-year-old man was robbed on a pathway near a Northampton primary school.
He was walking near Thorplands Primary School at about 6.20pm when he was approached by three men.
One of the men asked the victim where he was going, while a second man punched him to the ground. At that point all three offenders kicked and punched the victim and one of them rummaged through his pockets.
A passerby shouted at the robbers to stop and they all got onto bikes and rode off.
The victim was taken to hospital with facial injuries.
The first robber was white, 5ft 10ins, medium build, in his early 20s and wearing a dark-coloured coat or hooded top.
The second was of mixed race, 6ft 2ins, medium build, aged in his 20s and was wearing a turquoise coat or hooded top and grey bottoms.
The third was black, in his early 20s, 5ft 10ins, medium build and was wearing a dark-coloured hooded top and trousers.
Northamptonshire Police would like to speak to anyone who may have witnessed this incident or have any information regarding it.
Witnesses or anyone with information can call police on 101 or Crimestoppers, anonymously, on 0800 555 111.