Police are appealing for more information after the victim was pushed to the ground by three men in The Walks on Saturday night.
The victim, a man in his mid 20s, was approached from behind and pushed while the men tried to grab his rucksack at about 10.45pm.
He managed to run off without anything being stolen.
All of the attackers are described as being in their 20s. The first was approximately 5ft 7in and wearing a dark puffer jacket with a hat or hood. The second is 6ft 1in, of stocky build with short light coloured hair. He was wearing a dark jacket with a yellow or mustard coloured scarf or collar.
The third was 5ft 8in to 5ft 10in with short dark hair and was in a dark jacket and jogging bottoms.
Anyone with information is asked to call Det Con Emma Cross at Lynn CID on the 101 number or Crimestoppers on 0800 555 111.