Connor Godfrey, 21, is on trial in the NSW Supreme Court accused of murdering 43-year-old Giuseppe Pagano in a Haymarket serviced apartment building in the early hours of Easter Sunday in 2021.
Godfrey's barrister Mike Smith said it was disputed whether his client caused Mr Pagano's death.
Crown prosecutor Mark Hay told the jury Godfrey had just met Mr Pagano while walking down George Street from Circular Quay and was trying to source drugs.
He said CCTV footage capturing a physical altercation in a hallway would be difficult for jurors to watch, but central to determining whether Godfrey was guilty
"You're going to see a man lose his life," Mr Hay told the jury on Wednesday.
"You're going to see it several times."
The Crown alleges Godfrey put Mr Pagano in a chokehold that killed him by asphyxiation.
"One of the live issues in this case is that he says he was acting in self-defence," Mr Hay said.
Mr Smith told the jury the trained intent of the Brazilian jiu-jitsu "rear naked choke" move was "to put someone to sleep without inflicting any damage whatsoever".
Godfrey began training in the martial art when he was 14, although may have exaggerated his proficiency, the jury was told.
An autopsy revealed Mr Pagano had a potentially lethal dose of methylamphetamine in his system, which Mr Smith said had been injected shortly before dying.
He also had a heart condition.
Godfrey said he was acting in self-defence when police arrived within minutes of Mr Pagano's death.
He pointed out cameras in the hallway on level 13 of the Oaks apartment building he lived in on Castlereagh Street and told police to check the footage, Mr Hay said.
Mr Smith said Godfrey did not intend to kill, or even cause serious injury, to Mr Pagano, a much larger man.
"He does not strike a blow, does not punch, does not kick," he said.
"You may ultimately hear he had possession of a knife, which he did not use."
The prosecutor said CCTV footage would show Mr Pagano acting in self-defence, switching from "flight mode" to "fight mode", before he begins to "beat down" Godfrey.
"(Mr Pagano) starts laying punches down … all of them connecting in a serious way," Mr Hay said.
However, he said Godfrey overreacted even if it was in self-defence.
The lawyers' opening statements came at the end of a long first day for jurors, who were forced to evacuate the court shortly after being selected.
Justice Robert Cavanagh was in the middle of instructing the 15 jurors when an emergency evacuation warning sounded through the Darlinghurst Courthouse.
Two fire trucks attended before the public was allowed back in about 15 minutes later.
"It was a false alarm but obviously better safe than sorry," Justice Cavanagh told the jury when they returned.
The trial continues.
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