Gloucestershire Constabulary is appealing for witnesses to an incident on Longsmith Street in Gloucester on Wednesday 11 October.
The altercation took place between a motorcyclist and a pedestrian at around 3pm.
It's believed that the incident happened whilst the rider of the motorbike was heading towards the NCP car park. The male pedestrian jumped out in front of the victim and tried to steal the keys to his vehicle.
The victim, aged in his 40s, stopped his motorbike and was pushed by the offender; this caused his motorbike to fall on top of him which caused two breaks in his right leg.
The offender is described as a white male in his 50s- 60s and was around 5ft 8ins tall. He was possibly wearing glasses and was carrying a small shopping bag.
The offender may have come from the direction of Northgate Street before heading towards Bearlands.
Any witnesses to the incident are asked to call 101 or email email@example.com and quote incident number 281 of 11 October.