The accused, identified as Uday Kumar, allegedly struck his stepfather, Sridhar, three times with a motorcycle shock absorber.
He has been arrested in connection with the death.
Stepfather allegedly attacked mother
According to police, Sridhar had married Uday's mother, Deena, around 22 years ago after she separated from her first husband.
Uday was Deena's son from her first marriage and lived with the couple, along with Sridhar's two children, Darshan and Kanchana.
Sridhar, who worked as a journalist, allegedly had a drinking habit and frequently created a ruckus at home after consuming alcohol.
Police said he had also allegedly assaulted Deena during such quarrels.
The situation escalated on Tuesday night when Sridhar allegedly picked up a pair of scissors and attempted to attack Deena, police said.
Uday intervened and allegedly struck Sridhar three times with a motorcycle shock absorber.
Victim dies during treatment
Sridhar sustained serious injuries in the assault and was rushed to BGS Hospital, where he was undergoing treatment. However, he later succumbed to his injuries.
Following his death, police took Uday into custody and began questioning him about the incident.
Sridhar's body has been shifted to Victoria Hospital for a post-mortem examination.
The Madanayakanahalli police have registered a case and conducted a spot inspection. Further investigation is underway to establish the exact sequence of events and circumstances leading to Sridhar's death.