An elderly Christchurch man watched on in horror as his son was badly beaten in a road rage attack, police say.
The 37-year-old suffered serious facial injuries when he was allegedly attacked on Johns Rd in Harewood on Sunday morning.
He underwent surgery in hospital, and since mid-week has been recovering at home.
Detective Sergeant Mark Worner said the victim informed police of the incident only after he was released from hospital.
He had been driving with his 80-year-old father when the incident happened about 7.45am.
Mr Worner said a blue Isuzu Bighorn truck was driving "very slowly'' down Johns Rd, so the victim overtook the vehicle.