Joseph Esmaili, 24, was on Wednesday found guilty of manslaughter with a Supreme Court jury disregarding excuses he struck the blow in self defence.

The 41-year-old doctor was leaving Box Hill Hospital in May last year, heading home to his wife and children, when he stopped to tell a group including Esmaili to stop smoking near the front entrance.

An argument ensued, ending with the punch.

"I wasn't trying to hit him hard. I shouldn't have hit him in the first place," Esmaili told police during an interview recounted by prosecutors in court.

Esmaili said he felt pressured by the surgeon.

During a four-week trial the jury heard from witnesses who recounted the pair arguing and the subsequent sound of the punch and the sickening thud as the surgeon hit the floor.

"I saw and heard the noise of a tenpin bowling ball hitting the floor," one man told the jury.

Esmaili fled while staff from the hospital rushed to help their colleague.

Some were brought to tears when recounting evidence in front of Justice Elizabeth Hollingworth.

Nurse Jessica Bourke ran for help after viewing the scene through a window from a nearby stairwell

"I know he was punched and I ran up the stairs to get help," she said.

Mr Pritzwald-Stegmann's life support was terminated about a month later.

Defence lawyer John Desmond argued its withdrawal led to the surgeon's death, rather than the single punch.

He argued Esmaili had also felt threatened by the doctor who repeatedly pursued him after the initial argument and reacted in self-defence.

"My client is retreating," Mr Desmond said referring to CCTV footage.

"It's the doctor who continues to pursue. He puts down his bag. He's up for it."

Chief prosecutor Brendan Kissane QC argued the doctor would have ultimately died from the seriousness of his injuries.

Mr Pritzwald-Stegmann suffered bilateral skull fractures and was seen bleeding from the nose and mouth after the attack.

Esmaili will be sentenced at a later date.

Australian Associated Press