Former Aston Villa footballer Dalian Atkinson threatened to kill his elderly father in a "manic state" before he was Tasered by police, his brother said.
The 48-year-old died 90 minutes after he was hit by the stun gun in the street where he grew up in the Trench area of Telford, Shropshire, in the early hours of Monday morning.
According to relatives Mr Atkinson was suffering from a number of health issues and had a weak heart when he was hit by the weapon at around 1.30am.
The retired sportsman went into cardiac arrest in an ambulance on his way to hospital and medics were unable to save him.
The death is now under investigation by the Independent Police Complaints Commission (IPCC), the police watchdog who investigate all instances when a Taser is used.
Mr Atkinson's brother, Kenroy, 53, told The Sun the ex-Premier League star had undergone dialysis for kidney failure and was "not in his right mind".
He said his brother had attacked their 85-year-old father, Ernest, at his home on Monday before police were called to the scene.
"My brother had lost it. He was in a manic state and depressed - out of his mind and ranting. He had a tube in his shoulder for the dialysis and he had ripped it out and was covered in blood," he told the newspaper.
"He got Dad by the throat and said he was going to kill him. He told Dad he had already killed me, our brother Paul and sister Elaine and he had come for him. He was not in his right mind.
"We are all devastated. Our family is heartbroken."
Using barbed wires fired at a suspect, the shock delivered by a Taser can be thousands of volts in strength and is intended to immobilise.
On Monday Mr Atkinson's nephew, Fabian Atkinson, suggested officers would not have used the stun gun if they had known the ex-striker's medical history.
He said: "He had some health issues that he was trying to get through and that's why his heart was weak.
"When a Taser is deployed, as soon as a Taser is deployed, they need to automatically call an ambulance. How do they know the health of the guy or the girl that they are affecting?"
West Mercia Police said officers were called amid concerns "for the safety of an individual" and then deployed the stun guns.
Mr Atkinson was a top-flight striker in the 1990s, starting his career at Ipswich Town then playing for Sheffield Wednesday and Spanish side Real Sociedad before moving to Villa.
He scored 23 goals in 85 appearances for the Birmingham side between 1991 and 1995, before going on to play less successfully for teams including Turkish side Fenerbahce and Manchester City. He ended his playing career in South Korea in 2001.
Mr Atkinson's former friend and team-mate, Carlton Palmer, said he had struggled after his sporting career ended.
"It can be difficult for players when they finish and I know Dalian found it difficult," Palmer told Press Association Sport. "When you finish as a footballer, all of a sudden at 34 or 35 you have no routine and no structure to your life, and that can be a major problem. It can be a very dangerous spiral and unfortunately that's what it was for Dalian."
Mr Atkinson's death follows that of ex-soldier Spencer Beynon, who was Tasered by police in Llanelli, South Wales, in June after stabbing a dog and then himself.
Campaigners have raised concerns about the safety of the stun guns and called for restrictions on their use until more is known about the risks.
Police use of Tasers, which are intended as a non-lethal weapon, went up slightly last year with 10,329 uses by forces in England and Wales, a 2% rise on the previous year. However, of those, 19% (1,921) were discharges; a decrease of 3% from the previous year.