His friends took him to the home of a nearby paramedic - which is when the second accident happened.
"As they were driving out the driveway, a dog that was on the back of the ute leapt off and [Isaac], who was on the back of the ute, tried to grab him and fell off [and] his leg went under the back wheel."
The ute drove completely over Mr Strawbridge's limb, and he hit his head badly, said Mrs Walsh.
It was suspected that Mr Strawbridge had broken his leg, and a rescue helicopter was dispatched.
A Lowe Corporation Rescue Helicopter spokesman said a crew responded from Napier at 3pm and transported the men to Palmerston North Hospital.
Sam was discharged early yesterday morning with a cast on his leg, and Mr Strawbridge was kept overnight for observation due to knocking his head.
A MidCentral District Health Board spokesman later said Mr Strawbridge was also discharged yesterday.
Mrs Walsh said Sam, who has left school but not found a job yet, will be out of action for eight weeks.
"He's in a bit of pain but has all the medication.
"His bike's been locked away because he keeps saying that you don't need your right leg to ride. Some boys you can't keep down."
Mr Strawbridge, a farm worker, was required to take a week off work to recover.