CY WALSH has been found not guilty of murdering his father, Adelaide coach Phil Walsh, because of mental incompetence.

The 27-year-old had been accused of the stabbing murder of his father at their family home in Adelaide in July 2015.

In the South Australian Supreme Court on Wednesday, Justice Anne Bampton found he was not guilty of murder by reason of mental incompetence.

"I find he was suffering from a psychotic episode as a result of schizophrenia, which at the time of the conduct was undiagnosed," Justice Bampton said.

Cy Walsh stabbed his father 20 times and at least two of the wounds were fatal, the court heard.

He was not intoxicated by any drugs at the time of the stabbing, Justice Bampton said, accepting the forensic reports.

The judge found the objective elements of the case were established beyond reasonable doubt.

She ordered Walsh be subject to mental health supervision for life and it is likely he will be detained for some time at Adelaide's secure mental health facility, James Nash House.

A statement from his mother and Phil Walsh's wife, Meredith, was also read to the court in which she said she would continue to love her son.

"My heart remains broken. My daughter is also shattered," she said.

"We now all live the devastating consequences of a mental illness that was not understood.

"I will continue to love and support my son as his father has always done."