Hudson Martin was young, petrified and trying to defend himself from an imminent assault when he fatally struck a grandfather in the head on Christmas Day, his lawyer has told a jury.
He acted in self-defence when he grabbed a baseball bat during a street brawl almost three years ago and hit Anthony Clark, Martin's barrister Ashlee Cannon told a Victorian Supreme Court jury.
"This trial is all about a young 18-year-old man acting out of sheer fear that he is about to become the next person who is set upon," she said on Wednesday.
"He was frightened, petrified and acted to defend himself from an imminent assault.
"This is one of the clearest cases of self-defence you will see in a trial in this magnificent courthouse."
An argument over some illegal fireworks sparked a dispute between two groups in a street outside Mr Clark's Mooroolbark home, in northeast Melbourne, the court heard.
Shortly before 11pm on Christmas Day in 2019, Mr Clark was set upon by a group of eight young men, prosecutors told the court on Tuesday.
He threatened the group with a baseball bat and was ordering them to leave his property when Martin used the bat to strike Mr Clark's head.
Mr Clark, 50, fell to the ground and prosecutors alleged another man in the group kicked him, before they all fled.
He was taken to hospital, where he died three days later from a significant traumatic brain injury.
Martin has pleaded not guilty to manslaughter.
Prosecutor Mark Gibson KC alleged Martin hit the man over a misguided dispute, believing Mr Clark's relatives had assaulted one of their friends' mothers earlier over some illegal fireworks.
But Ms Cannon argued "fateful choices by a number of people" set off a chain of events that ended in Mr Clark's death.
She said Martin's story about that night had not changed since his six-hour police interview a few weeks later, and accused other witnesses, including Mr Clark's wife, of lying to police.
"Their credibility and reliability are very much an issue in this trial," Ms Cannon said.
The trial continues.