Newlywed Joe Kent probably suffered a cardiac arrest by the time he hit the ground after a fatal punch.
Luton Crown Court heard this week that the 25-year-old suffered a bleed to the back of the brain which disrupted his heart and breathing functions.
It resulted in the popular tattoo artist collapsing just seconds after receiving the punch, said neuro specialist Dr Saffa Al-Saraj in evidence.
Pleading not guilty to manslaughter is Samir Bostan, 25, from Middleton.
He and Hamza Noor, a 22-year-old from Wembley, are also pleading not guilty to assaulting Joe’s friend Andrew Curzon-Berners.
Bostan also denies assaulting Matthew Kent, the brother of Joseph, and causing him actual bodily harm.
The court heard how Joe and his wife Emma had gone out with family and friends last January to celebrate Emma’s 22nd birthday. The couple had married just five months previously.
They were queuing outside the Xscape’s KFC takeaway at the end of the night out when there was an “exchange of words” with three other men.
When one of the men insulted Emma Kent, Joe told him: “That’s my wife, you can’t say that’, the jury heard.
Bostan and Noor joined in an attack that was principally on Mr Curzon-Berners, but it is alleged Bostan also punched Joe twice.
After the first punch Joe was able to get to his feet and move normally. But after the second blow he was seen staggering away from the fight and moments later collapsed to the ground.
Dr Al-Saraj told the jury he had examined the deceased’s brain and also viewed CCTV footage of the incident.
He concluded that the impact of the second punch caused the young man’s head and neck to twist. This action damaged his vertebral artery, causing a tear and a bleed at the base of the brain.
“Collapse would have been within seconds,” he said.
Dr Al-Saraj said he had looked at 36 cases involving similar injuries. All 36 resulted in death.