The 11-minute video shows at least 14 officers piled on top of the half-naked black man in the city of San Francisco in California, Express reported.
One officer can be seen standing directly on his leg as he demands the return of his crutches.
The woman who filmed the shocking clip, Chaedria LaBouvier, said that police continued to hold the man down even when he was "restrained and clearly unable to walk".
In the video, LaBouvier is heard saying, "This is how you treat citizens? You're having him partially nude while you pin him down on his prosthetic leg?
"You don't protect and serve this community if that's policing to you."
San Francisco Police Spokeswoman Grace Gatpandan claimed officers found the 42-year-old man waving around wooden sticks and detained him for a mental health investigation as he walked toward street traffic.
Furious social media users slammed the clip and branded it an example of US police brutality.
Twitter user Karen Breakey said, "What every day racist policing looks like: unnecessary force, brutal disrespect and little humanity."
