The alleged attack is understood to have followed a row over a 70-cent phone call outside e-Times internet cafe and call shop on Dublin's Wellington Quay.
Zhen Dong Zhao (36), a Chinese man with an address at Jervis Street, has pleaded not guilty to murdering Dubliner Noel Fegan on May 20, 2011.
Mr Fegan (40) was originally from Finglas, but had been living in Aughrim Street. He had gone into the shop to phone his teenage daughter, who had sent him a 'Call Me' text.
John Bosco Dillon told the Central Criminal Court that he was in e-Times shortly before 4pm that afternoon.
"I became aware of a commotion over at the telephone boxes. Voices were raised," he said.
"When I looked up, I saw the deceased being chased by the accused," he said. "The deceased left the shop, followed by the accused," he said, adding that Mr Fegan had run straight out but had then turned right.
He later acknowledged that Mr Fegan had to turn because there were barriers between the footpath and the road. The court already heard that these barriers related to the visit of Queen Elizabeth that week.
"He took a right, which shortened the chase distance and he came within range of the accused," he said.
"The accused grabbed him by the collar and pulled him down to the ground."
He said that Mr Zhao then started to kick Mr Fegan.
"He kicked him two to three times and then the accused paused," said Mr Dillon, who explained that this was happening outside the window right in front of him and that he motioned at Mr Zhao to stop.
"He kicked him another two times," he added.
"He was lying in a 'C' shape and the accused was kicking his back," he continued. "I didn't see any kicks to the head."
Ruth Malone told the court that she was waiting for a bus outside the shop next to e-Times that day. She noticed something and looked up to see a man crouching over on the pavement with another man standing behind him.
"I saw the man behind then kick the man in front on his back," she said, explaining that this caused the crouching man to fall over.
"He was then kicked the second time on his lower back," she continued, adding that the man on the ground tried to stand but didn't fully succeed.
"The man behind kicked him at the nape of the neck," she said.
She said the victim fell down slowly while the attacker, who she described as Asian, walked back to the internet cafe at a normal pace. The jury was earlier shown CCTV footage of the 10-second-long incident.
The trial continues.