Troy Maxwell's stepfather had to wrestle an axe out of his stepson's hands and push him out the door following a violent episode where Maxwell assaulted his parents and damaged property.
The 23-year-old offender is under the Mental Health Act and suffers from a disorder on the autism spectrum, defence lawyer Richard Leith said.
The incident began after Maxwell smashed a ceramic mug on the driveway of the house he lived in with his mother and stepfather.
As Maxwell's mother tried to calm him down, he punched her in the head approximately three times. The stepfather, trying to push Maxwell away was then also punched in the head two to three times. He responded by punching Maxwell, police prosecutor Sergeant Rachel Willemsen said.
Maxwell's mother was in Whanganui District Court on Tuesday and wanted him to be bailed home.
Maxwell pleaded guilty to male assaults female, threatening to kill, assault by stabbing or cutting, common assault, and intentional damage.
Mr Leith said his client's disorder made him struggle to manage his emotions.
Judge Chris Sygrove granted bail and remanded Maxwell to May 11 for sentencing. A pre-sentence report was ordered.