A group gathered as police tackled the man
A full investigation will be held into the arrest of a man in Nottingham who was Tasered while on the ground.
The Independent Police Complaints Commission (IPCC) said a review of footage of the event had concluded it warranted greater scrutiny.
The incident took place early on Monday when four officers tried to restrain a man and used a Taser more than once.
The arrested man has said he intends to make a formal complaint but police said they had not yet received it.
Nottinghamshire Police said officers tried to arrest a 40-year-old man after being called out by door staff at one of the city's nightspots.
The man - who has asked to only be identified as Steve - said his memories of the event are not clear.
"You can see it all in the footage so take it from that. If I was unruly I was unruly, I don't know. All I remember was being punched and Tasered.
"The first thing I can recollect is being Tasered, when I could hear 'Taser! Taser! Taser!' that was the officers saying to the other officers to back off," he said.
The footage, taken by a cab driver, showed officers trying to arrest a man who was lying in the road outside Nottingham's Theatre Royal.
The Taser, which uses a 50,000 volt shock to disable a suspect, is apparently used at least twice.
The video was given to local radio station Trent FM and has also been posted on YouTube.
IPCC Commissioner Amerdeep Somal said: "Footage of this incident, which many people will now have seen, is of sufficient concern to merit a fully independent investigation.
"We would urge anyone who was present and witnessed this incident at any stage, from outside the nightclub to where the man was restrained, to tell us what they saw.
"We will want to look at any relevant CCTV footage of the incident as a whole as part of our thorough investigation. At the conclusion of our investigation we will make our findings public."
A police officer was assaulted, the force claimed, and needed hospital treatment. It also said it had voluntarily referred the matter to the IPCC.
Mick Taylor, of the Nottinghamshire Police Federation, said people needed to understand the demands of the job.
He said: "In relation to the number of times the person was Tasered, you are actually taught to keep Tasering them until they do what they are told to do.
"Clearly from the video we can see the officers are constantly speaking to the person."
The man was subsequently arrested on suspicion of causing grievous bodily harm and released on police bail.