A court heard Diane Jones, 62, died as a result of the blows inflicted by son Wayne Beer during the disturbance.
The incident happened at their home on Ambleside Road, Castleford, on March 14 this year.
-> 'Hand over your keys or we'll stab your kids' - Masked gang laughed as they threatened six-year-oldMrs Jones died a week later, March 21, as a result of the injuries she sustained in the attack.
Beer was charged with murder following the death.
Jurors were told that Beer was unfit to stand trial as he suffers from paranoid schizophrenia.
The jury found that Beer "did the act as charged" after hearing evidence.
Describing the incident, prosecutor Dafydd Enoch, QC, said: "This is an extremely sad case."
Mr Enoch said the attack happened when Mrs Jones went to try to calm her son down after he began "acting strangely."
The prosecutor added: "She was struck on the head by the defendant with the hammer on a minimum of eight occasions."
Beer then attacked Mrs Jones' husband, Terry, when he went to help after hearing his wife's cries for help.
Beer pushed Mr Jones down the stairs and threw furniture at him.
Mr Jones went to a neighbour's house for help and police were contacted.
Mr Enoch said: "The police came quickly but it was too late for Diane Jones.
"She was very badly injured. Her skull was fractured in several places."
-> Foreign Office contact family after Leeds man Sean Hercules dies in Spain Beer was outside the house when police officers arrived and he was detained after a struggle.
The prosecutor explained to the jury that it was an unusual case as they were not being asked to reach a guilty verdict in the case.
He said: "The only question, at the end of the day, you are being asked to consider is whether or not you can be satisfied, so you are sure, that he caused the injuries."
Mr Jones gave evidence at the hearing and described how Beer had been "shouting abuse" at his bedroom wall on the evening of the attack.
He said he went to get the phone to ring police as his wife went to speak to her son.
He said: "The next minute I heard Diane.
"She was shouting 'Terry he's hit me over the head' so I went rushing upstairs with the phone in my hand."
Mr Jones described how he ripped Beer's t-shirt during the struggle to stop him.
He continued: "He got hold of me and pushed me in the passageway and pushed me down the stairs.
"The last words she ever said to me was 'don't leave me here with him.'"
The jury heard a detective found Mrs Jones lying face down in a pool of blood on the bedroom floor.
A wooden-handled claw hammer was close by.
-> Man armed with meat cleaver tried to set fire to two banks in Hull The court heard Mrs Jones was unable to speak but she was able to communicate with the officer by squeezing her hand.
Beer was not in court during the hearing.
After reaching the decision, jurors were told that psychiatrists had diagnosed Beer as suffering from paranoid schizophrenia.
Enquiries are being made to see if there is a bed available for Beer at Rampton High Security Hospital.
The Recorder of Leeds, Judge Guy Kearl, QC, told the jury: "It is likely that in a case such as this that there may be a hospital order made to restrict the liberty of the individual by detaining them in hospital to receive treatment."
Beer will be sentenced on September 20.