Fifteen young men set upon a 39-year-old man in Wood Farm and kicked and punched him.
The man was left cut and bruised after the attack at 9.30pm on Monday on in Blackstock Close.
The victim was treated at the John Radcliffe Hospital and has since been discharged.
Investigating officer Det Con Darren Little, from Local CID at St Aldates police station, said: “I am appealing for who saw what happened or who may have been in the area and seen the incident to contact me.
“We believe there were up to 15 people involved in the incident, so if anyone saw a large group in the area around the time of the incident, I would like to hear from you.
“We believe the victim and the offenders were known to each other and so far there have been three arrests made.”
A three teenage boys from Oxford, aged 16, 17 and 18, were arrested on suspicion of assault causing actual bodily harm.
They have been released on bail until Sunday, September 21.
Anyone with information should call 101.
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11:20am Monday 28th July 2014
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