Mark Meredith was called by his son to ask for help with his scooter that had developed a fault on June 28, Wolverhampton Crown Court was told.
When he and his partner reached the scene they found that Michael Jadowski, a man they knew, was also there.
The 30-year-old claimed that the man’s son owed his mother £50 but Mr Meredith feared the defendant had taken Class A drugs in the past and was unwilling to give the money to him in case it was spent on a fix, Wolverhampton Crown Court was told.
Mr Meredith and his partner then drove off in search of Jadowski’s mother, explained Mr John Brotherton, prosecuting.
The couple stopped at her home in Pendeford, but got no answer.
Mr Meredith’s partner, who was driving, was leaving when she spotted the defendant coming down the path and came to a stop outside the address after turning the vehicle around in the street.
She did not realise until it was too late that he was armed with a knife and a crow bar, continued the prosecutor.
Jadowski attacked Mr Meredith who was trapped in the passenger seat by his safety belt and was struck with four blows.
He was cut on the wrist and forearm with both wounds needing stitches and later told police: “I knew he had a temper but had never had a problem with him before.
"If I had not put my arm across my chest he could have killed me.”
Mr Ian Windridge, representing Jadowski, of Eastney Crescent, Pendeford, said he had been diagnosed as schizophrenic and a history of violence, adding: “There were four blows inflicted within a very short time.”
The defendant, who had 28 convictions involving 49 separate offences, was found guilty of wounding and being in possession of two offensive weapons, and was jailed for two years.