A woman armed with a piece of glass was recorded being wrestled to the ground by three police officers as a police dog sank its teeth into her leg.
The incident was captured on mobile phone footage in Marian Square, Netherton, on Sunday evening, where members of the public could be heard expressing shock at the level of force used by officers.
However Merseyside Police said the arrest followed an attempt by the woman to strike one officer with a piece of glass and bite a second.
In the video there appears to be a stand off between the woman and three officers, who make a grab for her as she tries to walk into the road.
The dog can be seen to grab her right leg, while officers manage to force her to the ground.
The officers can be heard to shout "do not resist" in the full footage seen by the ECHO.
The woman, 29, was treated at the scene for a puncture wound inflicted by the German Shepherd type service dog and taken to hospital.
A police spokesman said the woman had called the force shortly after 7pm suggesting she was responsible for a previous offence and asking to be arrested.
However during the call, he said the suspect made threats to "harm members of the public and police officers" and claimed to be in possession of a knife and a knuckle-duster.
The force spokesman said: "Officers attended and requested the woman drop a broken piece of glass she was holding.
"When she refused, efforts were made to restrain her, during which she attempted to bite an officer and strike another with the glass.
"She dropped the glass when she was bitten to the right leg by a police dog, and was detained.
"A puncture wound to the leg was treated at scene by an officer before she was taken to hospital for further treatment to the bite."
The woman was discharged from hospital on Monday morning.
Police said they arrested a 29-year-old woman, of no fixed address, on suspicion of affray, possession of an offensive weapon, malicious communications, assaulting a police officer in the execution of their duty, causing unnecessary suffering to a service animal and threatening, abusive or insulting words or behaviour.
She has been released on bail while enquiries continue.