A row between two men in Banbury ended with one of them being assaulted.
Thames Valley Police is appealing for witnesses following the argument on Sunday.
At about 5.40pm, a 42-year-old man was assaulted outside the Yorkshire Bank in High Street.
The victim was hit, causing him to fall to the floor motionless, and the offender then rode off on his bicycle in the direction of Church Passage.
The man who carried out the attack was wearing a green top and may have been wearing shorts.
PC Pete Butt-Gow, from Banbury police station, said: "We are appealing to witnesses who may have information regarding this assault.
"Four to five young men are believed to have checked on the victim as he lay on the floor.
"We are keen to talk to them as they may hold information about the incident."
Anyone with information has been asked to contact police on 101.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here