A young father died taking part in a new internet craze known as “Punch 4 Punch”.
Tommy Main, 23, collapsed after trading heavy punches with another man in the violent “game” during a birthday party.
He was taken to hospital by ambulance in a critical condition, but died an hour later without regaining consciousness.
On Tuesday night his family lashed out at revellers who filmed the violent clash and its tragic aftermath instead of helping him.
Ben Main, 38, one of his three brothers, said they have been left “devastated” by the tragedy.
He said: “I can’t believe my little brother has lost his life. He was punched in the heart and it stopped beating. He died instantly. He’s got a little girl and she doesn’t know yet. How do you tell a three-year-old her dad is dead?”
Another brother, Roy Main, 36, slammed those who watched Main suffer the fatal injury. Writing online, he said: “For the people that was at the party that can see this call yourself friends… you should have stopped it not try and film it.”
“Punch 4 Punch”, which began in the US, is the latest reckless game of dare to take hold of the internet. It involves two contestants exchanging blows until one gives up, often having to take a forfeit by drinking alcohol.
Social networking sites are full of photographs of young men showing off bloody cuts and large bruises after exchanging punches, often while being filmed.
The tragedy echoes the “neknominate” drinking game which has claimed several young victims who were dared to drink huge amounts of alcohol.
Main, who worked for his father’s removal firm, collapsed shortly after midnight on Sunday morning at a 16th birthday party at a house opposite his home in Erith, south-east London.
Witnesses said he traded several blows with another man, 20, before falling to the ground after a heavy blow to his upper chest.
The 20-year-old man was arrested on suspicion of murder and has been released on bail until September.
Detectives were on Wednesday treating the death as “unexplained”.
A post mortem examination was inconclusive, and it may take months for forensic tests to be completed.