The blow was so hard that his friend who was facing the other way heard it, and turned around.
Mr Mohamed Ayub Shaik Dawood took the stand in court yesterday, and recounted the events of September 2014.
It was around 1am on Sept 22 when he witnessed an altercation between cabby Chan Chuan Heng, 47, and Norwegian Arne Corneliussen, 51, at the intersection of Circular Road and North Canal Road. Mr Ayub said he saw Chan deal the first blow in the incident.
"It was a hard one (hit)," said Mr Ayub, and so loud that his friend, Mr Roslan Zainal, who was facing away, turned around to ask what the sound was.
He said: "I told him that the cabby had hit the Caucasian man."
The case made headlines last year after a dramatic turn of events.
Mr Corneliussen, a Singapore permanent resident, had initially been sentenced to 10 weeks in jail, after pleading guilty to causing hurt by grabbing Chan's neck and choking him following a night of drinking.
However, a few weeks later, Mr Ayub and Mr Roslan came forward to claim that Chan, and not Mr Corneliussen, was the aggressor in the incident.
The guilty plea and sentence was quashed, and the case was sent back to the State Courts for a retrial, where Mr Corneliussen was fined $2,000 for a lesser charge of causing hurt by wrapping his arm around the cabby's neck.
Chan was then charged with voluntarily causing hurt and providing false information to the police.
Yesterday was the first day of Chan's trial and three witnesses, including Mr Ayub and Mr Corneliussen, took the stand.
Chan turned up in court with his wife and another family member, and was expressionless throughout.
Mr Ayub, a valet at The Fullerton Hotel, told the court he had seen Chan and Mr Corneliussen talking next to Chan's parked taxi at Circular Road while he and Mr Roslan were trying to hail cabs after his work.
He said he was standing across the road and could only see the men's bodies from chest down, as the taxi was blocking them.
He said: "I wasn't able to hear the beginning of the conversation until the Caucasian man raised his voice and said, 'Why so expensive? You want to cheat me?'."
He added Chan then turned to face Mr Corneliussen, hurled vulgarities and used his right hand to hit the Norwegian on the left side of his head.
Mr Ayub said he didn't see Mr Corneliussen hit Chan.
Mr Ayub came forward as an eyewitness last year after he read The New Paper report about the incident and realised that he had witnessed it a few months ago.
He decided to talk to Mr Corneliussen's lawyer, Mr Terence Seah from Virtus Law, when he noticed the account in the news report differed from what he had seen.
Yesterday, defence lawyer Steven Lam tried to challenge Mr Ayub's claims that he had a clear view of the altercation between the duo, as the taxi was in the way.
Mr Lam also asked if it was possible that Mr Ayub had only noticed the duo after Mr Corneliussen raised his voice, as he might have been busy looking out for a taxi.
But Mr Ayub was adamant that he had seen the exchange clearly from the start.
Video from Chan's in-car camera was shown in court.
The clip showed Mr Corneliussen chasing Chan across the road twice and Mr Corneliussen gesturing and shouting when a crowd gathered, with members of the crowd doing the same.
Mr Corneliussen, who is unemployed, was the first witness. He told the court he had six to seven drinks that night and was looking for a taxi. He got upset when the cabby suggested a flat fee of $45 to take him to his home in East Coast.
"I said I would report him to the LTA (Land Transport Authority)... He got upset and told me to f*** off, and we had a few words going back and forth.
"That's when there was a stinging pain at the side (of my head) and everything went black," he said pointing to the left of his forehead.
Mr Corneliussen said he was convinced Chan had hit him, but couldn't recall chasing him. He said he only remembered "some kind of commotion" where there was a crowd and a lot of screaming.
He believed he was the aggressor after watching a video of the incident and being told by the police that there were eyewitnesses.
Before his first conviction last year, Mr Corneliussen met Chan and gave him $30,000 as compensation.
The doctor who signed off on Mr Corneliussen's medical report at Changi General Hospital where Mr Corneliussen had gone for a check-up hours after the incident, also took the stand.
Dr Peter Looi said it was possible for Mr Corneliussen to suffer temporary memory loss and only remember "bits and pieces" if he was struck on the head.
Chan's lawyer asked if it was possible for one who was stunned by a blow to the head to have a good memory of when he was struck, but loss of memory afterwards.
Dr Looi said: "I think not likely. I wouldn't know, but not likely."
The trial continues today when two more witnesses will be called to the stand.
- See more at: http://www.tnp.sg/news/singapore-news/witness-cabby-struck-passenger-so-hard#sthash.lhuyOkT2.dpuf