An Adelaide man accused of murdering a young father outside a suburban shopping centre did not intend to kill the victim and inflicted the fatal stab wound as a "half-hearted warning shot", his lawyer has told the Supreme Court.

Key points: Alexander Watts, 25, was fatally stabbed in April of 2017

Alexander Watts, 25, was fatally stabbed in April of 2017 Accused killer Shaun Falkiner pleaded not guilty to murder

Accused killer Shaun Falkiner pleaded not guilty to murder His lawyer told the court his client did not intend to kill and was in a "state of fear"

Shaun Falkiner, 28, is on trial in Adelaide's Supreme Court charged with murdering 25-year-old Alexander Watts.

Mr Falkiner is accused of fatally stabbing Mr Watts in the abdomen outside the Elizabeth Shopping Centre in April last year with a long-bladed knife he stole from a supermarket.

The court heard about 25 minutes before the fatal attack Mr Falkiner had a confrontation with a woman he knew in the shopping centre.

During the confrontation Mr Falkiner pushed the woman after she slapped him in the face and she told him "you're dead, I'm calling my ex".

The court heard that Mr Falkiner then went to Woolworths and stole a kitchen knife with a 20-centimetre blade.

On Wednesday defence lawyer Bill Boucaut told the jury the woman's ex, who was known by the nickname 'Kiwi', had bashed his client on a previous occasion.

Alexander Watts died after he was stabbed in the chest at the Elizabeth shopping centre in Adelaide in 2017. ( Facebook )

"Clearly there is a bit of history between the accused Falkiner and this bloke Kiwi," Mr Boucaut said.

He said Kiwi was a physical threat to his client, who weighed 65 kilograms.

"Plenty has been said about his size … It's obvious he is a man mountain; six foot four, 185 kilograms," Mr Boucaut said.

"Kiwi you would think, quite reasonably, would crush the accused like a fly if they happened to face an altercation."

The court previously heard Mr Watts was friends with the woman who threatened Mr Falkiner and that he started following the accused through the shopping centre and "angry words" were exchanged.

On the prosecution's case, just before Mr Falkiner approached Mr Watts on the pedestrian crossing outside the shopping centre and stabbed him, the accused's girlfriend said "you are weak", and "just do it".

Lawyer says accused was in 'state of fear'

Mr Boucaut told the jury that when his client stabbed the victim he was in a "state of fear" and believed he was being hunted down.

"The accused genuinely believed it was necessary and reasonable to defend himself," he said.

"He has gone up and given a half-hearted warning shot … there is no doubt whatsoever this man was scared of Kiwi and what was going to happen and that's what brought all this about.

Loved ones placed flowers at the Elizabeth shopping centre in Adelaide's northern suburbs. ( ABC News: Shuba Krishnan )

"That is self-defence, members of the jury."

Mr Boucaut said his client did not intend to kill Mr Watts as the prosecution alleged.

"If he had a murderous intent, you might think that it's quite remarkable that he inflicted merely one stab … one very quick stab, he doesn't go on with it," he said.

"If the accused wants Alex Watts mortally wounded, grevious bodily harm inflicted upon him, or killed, you'd expect him to have another go because at that stage the deceased is still upright, he is still walking."

The trial before Justice Trish Kelly and a jury of 12 continues.