Police officers have been removed from usual duties after concerns over the use of force in a video circulating on social media.
The footage shows an officer using a baton after a row breaks out between a man and plain-clothed policemen in Upper Sutton Street, Aston, Birmingham.
West Midlands Police said it was “treating this matter seriously”.
It said officers on film would “not be deployed on usual duties” while an internal investigation took place.
The video was posted on Sunday by police monitoring campaign group Netpol.
In a statement, West Midlands Police said: “We are aware of a video circulating on social media relating to arrests made by officers in Birmingham yesterday.
“We are quickly gathering as much information as possible and we will undertake an assessment of that information to understand exactly what has happened.
In a tweet, community campaigner Desmond Jaddoo, said: “This not the way to conduct stop & search or treat the public.
“Excessive disproportionate unjustified use force against the BME (black minority ethnic) community.”
The force said a 20-year-old man arrested for a public order offence had been released released while inquiries continue.
A 28-year-old male was cautioned for possessing cannabis.