Steven John Johnson is standing trial for murder in the NSW Supreme Court in Tamworth after a jury was empanelled on Tuesday morning.

The now-39-year-old has pleaded not guilty to murder, manslaughter, assault causing death while intoxicated and assault causing death of 52-year-old Kenny Matthews in Tamworth, almost two years ago.

The pair were allegedly involved in a punch-up about 7pm that spilled onto Goonoo Goonoo Rd after a drinking session in a Bilkurra St unit on Friday May 15, 2015.

On the opening day of the trial, the jury was told Mr Matthews died in Tamworth hospital the following day as a result of internal bleeding into his abdominal cavity after small lacerations to his spleen had increased.

Crown prosecutor Lee Carr said the crown’s case against Johnson relies upon “an intention to inflict grievous bodily harm … really serious harm”.

He said eye witnesses would give evidence that Mr Matthews was attacked, and punched and kicked multiple times along Goonoo Goonoo Rd, causing the injuries, and ultimately his death.

“Small lacerations to his spleen, the crown says were as a result of blunt trauma … by the accused on the previous afternoon of 15th May, 2015,” Mr Carr told the jury in his opening address.

The court heard Mr Matthews did not seek medical treatment until he was taken by ambulance to hospital on Saturday about 1.30pm.

The court heard Mr Matthews “was not a healthy man” and suffered several conditions because “he abused alcohol”.

Mr Carr said Mr Matthews had eight litres of blood in his abdonimal cavity which was “grossly enlarged”.

An average male adult spleen was about 140g in size, but Mr Matthews’ was 1.2kg, the court heard.

“It was grossly effected by alcohol,” Mr Carr told the jury, later adding that doctors said the bleed in the abdomen was “significant, very serious, life-threatening”.

“The chance of stopping the bleeding because of his various conditions was next to none.

“The doctors decided that they would not do any operative treatment.”

Defence barrister Chris Taylor said the defence case centred around several issues, including that the accused acted in self-defence when he was allegedly set upon by Mr Matthews, and that the deceased had refused medical treatment on the night of the alleged fight.

Mr Taylor told the jury that for 12 hours after he left the scene of the altercation, Mr Matthews drank alcohol and took methamphetamine and cannabis, but there was a period where he was alone.

He said the deceased “was in effect unaccounted for … when he left the scene to source drugs … to score some pot".

Mr Taylor said the injuries to the deceased could have occurred then if he had “fallen over”, or even prior to the altercation, and would call evidence to that effect.

Mr Matthews died the night after the street fight in hospital but not before he gave police an interview, telling them he had allegedly been assaulted by Johnson.

The court heard two witnesses to the fight were Johnson’s sister, Shannon Johnson, and Stephen James Johnson, who is known as “Spider” to friends, and is four years older.

Mr Matthews told police it was the older of the Steven Johnson’s who assaulted him, but it’s the crown’s case that was “a mistake”, with photographs of the pair to be tendered in the trial.

The court heard Ms Johnson and Mr Matthews had purchased six “long-necks of alcohol” from a bottle shop nearby earlier in that day, before the pair, along with the accused, purchased a 4.5 litre cask of wine and a cordial or fruit mixer to go with it just before 6pm.

The court heard the accused and deceased, along with the “Spider” Johnson and Ms Johnson consumed about 3L of the cask before the accused allegedly forcibly dragged Mr Matthews out of the house when an argument erupted.

The jury was told more than 40 witnesses are expected to give evidence in the trial expected to run for five weeks in Tamworth.

The trial continues before Justice Richard Button.