An investigation is under way after police in Nottingham shot a man three times with a taser stun gun as they tried to arrest him.
A member of the public filmed the incident, which happened in the city centre in the early hours of Monday, and passed the video to Sky News.
The witness told Sky's radio colleagues at Trent FM that the man had already been shot once with the taser before he started filming.
He is seen wrestling on the ground with two police officers, one of whom points the stun gun at the man and fires it, causing him to briefly lie still.
The suspect begins to struggle again and within a few seconds two other policemen arrive at the scene.
Then the officer armed with the stun gun shouts: "Taser, taser, taser", as he fires the weapon for a second time.
His colleague is later seen punching the man several times in his upper body, while shouting: "Release your arm!"
In a statement, Nottinghamshire Police said its officers had responded to a call for assistance from door staff to help deal with an aggressive customer.
One officer was assaulted and required hospital treatment as police dealt with the incident.
A 40-year-old man was arrested on suspicion of grievous bodily harm and was released on police bail.
Nottinghamshire Police said the footage had been voluntarily referred to the Independent Police Complaints Commission (IPCC) for investigation.
Assistant Chief Constable Peter Davies said: "We understand that some members of the public may be concerned about this.
"The public's trust and confidence is very important for us, which is why we have referred this matter for an objective investigation to the IPCC.
"We are proactively looking at other CCTV in the area to ensure we have a clear picture of events leading up to the arrest and I would ask anyone in possession of such evidence, including the person who took the footage that has been published, to come forward as witnesses."
Last month the Home Office announced that an extra 6,000 taser stun guns were to be handed out to police in England and Wales.
The roll-out follows a 12-month trial in which the weapon was used by frontline officers in 10 forces.
The Home Office claim tasers are a powerful deterrent in preventing escalations of violence.