The police watchdog is looking into claims officers used excessive force during arrests in Birmingham.
The Independent Police Complaints Commission (IPCC) said it had launched a probe after mobile phone footage was released on social media of two men being arrested.
The footage shows an officer using a baton after a row breaks out in Upper Sutton Street, Aston, on Sunday.
The IPCC said it is investigating after a referral by West Midlands Police.
IPCC Commissioner Derrick Campbell said: "We are conscious of the concern this video footage has caused and the impact on public confidence in policing such an incident can have.
"We have now started an independent investigation which will look thoroughly at the use of force by officers."
On Monday the force said the three officers - who were in plain clothes at the time of the arrest - have been redeployed to other work.