A police force said it was reviewing CCTV footage after a student who was arrested claimed he was repeatedly assaulted by an officer.
Northamptonshire Police said the man was questioned in relation to drug supply offences but was released without charge.
The student told the BBC he had stopped to give change to a homeless person when a man in a hoodie, who he later realised was a police officer, ran towards him.
The incident was filmed by a friend, and appeared to show him being hit several times while on the ground.
He has made a formal complaint and said the officer should be disciplined.
As first reported by The Shade Borough, the 22-year-old student, known as Samuel, said he was walking down Northampton's Barrack Road on 8 August when he stopped to give change to a homeless person he had met before.
He said: "As I was walking off, I just felt something walking towards me. It was a white man in a black hoodie.
"I admit, I did run, but I stopped because I realised it was a policeman and apologised.
"So I'm thinking I'm just going to be arrested or whatever, but I was hit, and hit, and hit, and I was thinking 'this is unbelievable'."
He said he was "smashed towards a wooden gate", before losing his balance and falling to the floor, where he alleged he was beaten up.
Northamptonshire Police said they were aware of the CCTV footage and were talking to Samuel to discuss his concerns.
The force added the incident was being reviewed internally, including assessments of officers’ body-worn cameras.
They said the stop was made after a person was seen to exchange a package, which was suspected to be related to potential drugs supply offences.
A spokesman added: “When officers approached to conduct a stop search, the man ran off, resulting in a short pursuit before he was apprehended.
"Following a negative search, the man was released with no further action."
Samuel wants to take the matter further and would like to see the officer "face some kind of disciplinary".
He said: "I've hired a solicitor, Miriam Altaf, she's working very hard to bring me some kind of justice.
"We've filed a complaint against Northamptonshire Police and we've also contacted the IOPC [Independent Office for Police Conduct].
"I was complying with the officer, I didn't commit any crimes."
"I couldn't believe I was the victim of such brutality from a police officer," Samuel added.
"I asked myself if I would have been treated the way I was treated if I wasn't of ethnic minority."