He skidded across the grass verge, hit a chain-link fence, narrowly missed an innocent car, smashed into a concrete culvert which propelled the car into the air, and spun 360 degrees.
Brother Lawrence, who was not wearing a seatbelt, was thrown out of the passenger window, landing on the road.
Le Grys, who was following just behind, couldn't stop his speeding car and avoid hitting Lawrence.
He ran over him.
Fearing he had "just killed someone", Le Grys fled.
Lawrence suffered "quite horrific injuries", Christchurch District Court has heard, including an unstable fractured pelvis, a fractured left collarbone, and punctured lungs.
He spent several days at Christchurch Hospital. He is now back at work.
Other motorists who were nearly entangled in the pile-up were left "traumatised" by what they experienced, the court heard.
Le Grys earlier pleaded guilty to charges of being party to operating a motor vehicle in a race causing injury and failing to stop and ascertain injury after a crash.
It was only "an absolute quirk of fate" that the crash was not fatal, the court heard.
Judge Brian Callaghan told Le Grys today that he was indeed lucky not to be in court on a manslaughter charge or one of death by dangerous driving.
The judge said that boyracer legislation introduced in New Zealand over recent years is designed to try and prevent this type of event.
Defence counsel Kirsty May said Le Grys, who now hopes to start a building apprenticeship, is "extremely remorseful".
He has since swapped his car for a bicycle, she said.
Lawrence Barrett is "amazingly forgiving" and doesn't bear any malice towards either his brother or Mr Le Grys, the court has heard. He accepts he should've been wearing a seatbelt.
Joseph Barrett, a Christchurch machine operator, was earlier sentenced to two months' home detention after admitting a charge of driving on a restricted licence, and dangerous driving and causing injury to his brother, Lawrence.
Judge Callaghan suspected that Le Grys' youth had a lot to do with the incident.
He sentenced Le Grys, who was supported in court by his father today, to four months of community detention, with restrictive curfew hours including Monday to Friday 7pm - 6.30am.
The judge also ordered that Le Grys pay $1000 in emotional harm reparation to Lawrence Barrett, at a rate of $100 a fortnight.
Le Grys is also disqualified from driving for 12 months.
