A police officer shot an unarmed man with his Taser because he was worried he might have a knife and took "one step too far" towards him, an inquest has heard.
Pc Terence Donnelly said he had warned Jordan Begley to stand still and not to move so he could be searched.
But the officer told the hearing he opened fire with the stun gun after Mr Begley put his hands in his jogging pants' pockets and walked towards him.
Mr Begley died in hospital after being Tasered and restrained when police were called to his home in Gorton, Manchester, during a row with neighbours on July 10 2013.
At least 11 officers from Greater Manchester Police (GMP) rushed to the scene after Mr Begley's mother Dorothy dialled 999 to say her son was involved in a row and had grabbed a knife, the jury at Manchester Civil Courts of Justice heard.
Mr Begley, who worked in an ice cream factory and was a heavy drinker and a cocaine user, had thrown the knife down and was unarmed when police arrived following the "Grade One" emergency response prompted by the report of a knife involved in the incident.
Pc Donnelly joined colleague Pc Andrew Moore in the dining room of the house with Mr Begley, who he described as "angry" and shouting at officers to get out of his home.
Pc Donnelly told the hearing: "I told him we have received a call with somebody with a knife, just need to make sure it is not you, or words to that effect.
"He just seemed to be ignoring me."
The officer said Mr Begley then walked towards him about half way up the length of a dining table so he got his Taser out of its holster and aimed it at Mr Begley.
He continued: "I told him Pc Moore is going to search him and any sudden movements towards him or me and I will activate the Taser. He took a step towards me at that point."
Marc Willems QC, counsel to the inquest, asked if he felt that was a "provocation".
The officer replied: "It got me worrying at that point."
Pc Donnelly continued: "I repeated, 'Stand still! Taser officer. Stand still! Show me your hands.'"
Mr Willems asked: "Did he?"
Pc Donnelly replied: "No. He steps again. I took a small step backwards. He then took a quicker step, a quick step towards me. That's when I fired the Taser."
Mr Willems asked if Mr Begley had taken "one step too far" and he then pulled the trigger.
"Correct," Pc Donnelly replied.
Earlier the officer said that before going into the house, while talking to Mrs Begley outside, he got the impression the weapon involved had been a steak knife.
The jury have seen photos of the knife in question, later found on a kitchen top, a smaller kitchen knife which Mrs Begley said she used to peel potatoes.
After the Taser was used, four or five armed police officers "burst" in to restrain and handcuff Mr Begley, who struggled with them, and Pc Donnelly and Pc Moore left the room.
Pc Donnelly added: "That's when I realised something had gone wrong or something was happening in that room. I was worried because I knew something was happening."
Mr Begley had begun to struggle to breath and slipped into unconsciousness. The armed officers went from restraining him to giving emergency first aid and calling an ambulance.
He was taken to Manchester Royal Infirmary where not long afterwards doctors told his mother her son had died.
The jury have heard that expert medical assessments concluded Mr Begley suffered a cardiac arrest approximately two minutes after the Taser was deployed but it did not or was "unlikely" to contribute to or cause the heart attack he suffered, which was more likely linked to alcohol intoxication and the stress of being restrained.
Mr Willems asked the witness about a series of documents to do with police training, using Tasers, threat assessments and tactical options, referencing guidance from the College of Policing, the police's "Conflict Management Model", Acpo guidelines, GMP procedures and the Human Rights Act.
Mr Willems said the rules state the use of force must be minimum, proportionate, reasonable and non-discriminatory.
He continued: "Use of force must be an honestly held belief it is absolutely necessary. Is that what you understand to be the case?"
Pc Donnelly replied: "Yes."
The hearing continues.