Kevin Robert Fulton, 46, is on trial in the High Court at Invercargill.
The jury was shown CCTV footage of the incident from January 28, 2023, which caused lethal injuries to the victim.
After Fulton told Mr Watson he could not bring his drink into the courtesy coach, the victim threw his bottle across the carpark.
The footage showed Fulton ducking away from the vessel as it came in his direction.
The defendant responded by grabbing Mr Watson from behind in a restrictive hold.
Less than a minute later, Fulton pushed the defendant in the chest, causing him to fall to the ground.
He hit his head on the concrete, causing a brain injury which ultimately led to his death three days later.
Yesterday, the Crown and defence lawyers summed up.
Justice Jonathan Eaton directed the jury to consider the critical issue of why the defendant pushed Mr Watson.
"This whole course of conduct stems from the deceased, Mr Watson, throwing a bottle, I say at Mr Fulton [and], that Mr Fulton was the target of that violent action," Mr Young said.
"Mr Watson was ... upset and angry at the people who pointed out that you can’t take alcohol in the coach."
Fulton gave evidence that he was expecting Mr Watson to hit him, and was worried he might "lash out" inside the van.
"If he’s prepared to throw a stubby at me ... he could be prepared to start lashing out too," he said during the trial.
After Mr Watson threw the bottle, Fulton restrained him and yelled for someone to get the manager.
"Seeking the assistance of the manager shows that Mr Fulton was acting with pure motives. He was genuinely trying to diffuse the situation," Mr Young said.
Crown prosecutor Mike Brownlie argued Fulton was acting out of anger and frustration, not self-defence or to prevent a breach of the peace.
"He just wanted a ride home; he just wanted to get in the coach ... and then next minute he is on the ground," he said.
"Sure he might’ve wanted to take a sneaky vessel on the coach on the way home ... yes, it was against the rules."
During the trial, the jury heard evidence that Mr Watson was yelling "how f...ing old are you?" after he was released from Fulton’s grip.
"He had just been manhandled by someone decades younger than him," Mr Brownlie told the jury.
The Crown said the assault was unnecessary and non-violent resolutions had been available to the defendant.
"The defendant knows this older man simply wants to get into the courtesy coach to go home. The defendant won’t let him in."
He said Fulton must be found guilty as there was no threat perceived.
"[The defendant] was a local, this was his turf and he decided that the deceased didn’t deserve a ride home," Mr Brownlie said.
"The reason he pushed him is simply because he did not want him in the courtesy coach."
The jury was deliberating overnight.
