Police prosecutor Sergeant Neil Coker said Greville was travelling "well above the posted speed limit" at about 91km/h when he braked heavily and skidded about 50m, before colliding with the rear of a 74-year-old woman's vehicle, shunting it off the road.
The victim received heavy bruising to her face and ribcage and was taken to Hawke's Bay Hospital, and later discharged.
Greville stated he was "very remorseful" and that he had been "showing off," Mr Coker said.