The 64 year old - who can't be named - was jailed on serious assault and wounding charges in Brisbane District Court after losing his temper and grabbing a knife while visiting family on December 27 2020.

He was outside his stepdaughter's home north of Brisbane with a nine-year-old grandchild who had a water pistol when "bad blood" boiled over, the court was told on Wednesday.

The child accidentally sprayed water inside the house, interrupting a card game between the stepson-in-law, the step daughter and their other son who was aged seven.

The upset stepson-in-law reacted by shutting a nearby glass door and locking it with the grandfather and child still outside.

The grandfather entered the house via another door and confronted the stepson-in-law who had returned to the card game, repeatedly asking "what did you say?".

The stepson-in-law did not respond. He also did not notice the grandfather now had a knife in his hand.

The 64 year old grabbed the stepson-in-law by his ponytail and stabbed him in the chest before putting the blade down and punching him twice in the head.

The stepson-in-law fell to the ground on all fours before being hit in the back of the head, sustaining a cut to his neck.

"There was previous bad blood between the two because of a previous incident," crown prosecutor Ryder Reid said.

The stepson-in-law was taken to hospital where he was kept in intensive care overnight after being treated for bleeding in the lungs.

He returned to hospital on January 2 2021 and stayed for another five days when his chest wound became infected and required surgery.

"The defendant had a knife in his hand before approaching ... and effectively took him (stepson-in-law) by surprise," Mr Reid said.

"The offending was entirely disproportionate to any conduct that preceded it ... it was irrational behaviour."

The grandfather described his behaviour as "not only out of character but also an over-reaction", his defence said.

He had a New Zealand criminal history with a series of assault offences from 1975 but had become a family man since his last matter in 1997, the court heard.

Family members including his grandchildren were present in court when he pleaded guilty to two domestic violence offences - wounding and assault occasioning bodily harm.

They became upset when Judge Jodie Wooldridge sentenced him to two years and nine months in jail.

He will be eligible for parole in January 2023.

"At no time had the complainant exhibited violence or aggression to you before you commenced your assault on him," Judge Wooldridge said.

"It is fortunate that the complainant was not more badly injured."

Australian Associated Press