The police officer accused of killing Ian Tomlinson was "making an example of him" when he struck him with a baton and pushed him to the ground, a court heard today.
Southwark Crown Court was read a statement from American businessman Christopher La Jaunie, who filmed Pc Simon Harwood hitting the 47-year-old.
Mr Tomlinson died on the fringes of the G20 protests in the City of London in April 2009.
He was facing away from a line of police officers when he was hit, and walked 70 metres before he collapsed and later died.
Prosecutor Mark Dennis QC read Mr La Jaunie's statement, which said: "Mr Tomlinson was not posing any threat to the officers prior to this, or aggravating them.
"I had the impression that the officer was making an example of him."
The businessman came forward with his footage after Mr Tomlinson's family appealed for information, the court heard.
Initially a pathologist found that he had died of natural causes, having suffered a heart attack, but later reports suggested internal injuries led to his death.
Mr La Jaunie said Mr Tomlinson was "bumping along" the line of officers, trying to get through.
He said: "I couldn't understand why he was getting so close to the police line. I thought they might see this as some kind of a threat.
"I didn't see him as a protester, I had the impression that he was just intoxicated and a bit out of sorts, just trying to get home."
Giuseppe Di-Cecio, who worked nearby, said Mr Tomlinson did not look like a threat to the police.
He told the court: "It was a bit harsh, what we commented at the time was that it was a bit harsh because this guy didn't look like a threat at all. He was not in a crowd, he was kind of isolated.
"He was not making physical contact with the officer who pushed him.
"Mr Tomlinson fell heavily on the ground, so we thought he might have injured himself."
Harwood, 45, from Carshalton in Surrey, denies manslaughter and maintains that he used reasonable force.
Protester Alan Edwards said Mr Tomlinson went "flying through the air" when he was pushed, and only just managed to take his hands from his pockets in time to try to break his fall.
Another demonstrator, Joshua Fenech, told the court police officers stood "nonchalantly" after Mr Tomlinson was knocked to the ground.
"They weren't interested really. They were just having a chat amongst themselves, they didn't offer any assistance even though he was on the floor in obvious distress."
Around 15 minutes before hitting Mr Tomlinson, Harwood had tried to arrest a protester who managed to wriggle free in front of a jeering crowd, jurors heard.
He saw the man, dressed in black, writing "all cops are bastards" on the side of a police vehicle in Cornhill.
Constable Andrew Hayes, who was driving a police carrier that day, said Harwood was "almost in a tug of war" with the man as other protesters pursued him down the street.
He said: "There was jeering going on and I felt at that point the crowd was chasing Pc Harwood down the street.
"Since he had taken hold of the person in black it had become more hostile and was directed towards Pc Harwood.
"The gentleman that he had hold of wiggled out of his jacket, and left Pc Harwood holding the jacket."
Jurors were played film footage of the man being marched past Pc Hayes' carrier, and colliding with the driver's door to jeers from the crowd.
Pc Hayes said: "I've gone to get out, opened the driver's door and something collided with the driver's door.
"I could see it was Pc Harwood and the person in the black."
Around 15 minutes later Harwood, from Carshalton in Surrey, encountered Mr Tomlinson near the Royal Exchange buildings.
In a previous statement, Pc Hayes said the crowd was aiming kicks and punches at Harwood as he attempted to make the arrest.
Today, a film clip was played showing one man apparently trying to trip him over as he struggled to keep hold of the protester.
Earlier, the court heard from witnesses who saw Mr Tomlinson as he blocked a police van in Lombard Street shortly after 7pm.
Passer-by James Stone said he looked "gaunt with glazed eyes" and was "very slow to react", looking "dazed and confused" when police officers told him to move on.
Later, Constable Andrew Brown turned Mr Tomlinson away from a cordon in King William Street that blocked his route home to Smithfield.
In a statement read to the court because Pc Brown has since died, he said: "The reality of the situation escaped him. I told him that he could not go past me. He stared at me, not in confrontation or disbelief but in incomprehension."
The trial continues tomorrow.