Truck was placed in Park on an inclined road. Exiting truck, truck started to roll backwards. I was struck and right foot was run over by Driver's side front tire and knocked down. I was wearing composite toe shoes which enabled me to get up and run after the truck, trying to stop and control the truck a second time. I was hit again and thrown off the side of the road into a briar patch. Truck continued to roll backwards and off the road into the woods. Upon investigation, two separate County Deputy Sheriffs confirmed that the truck. when it came to rest, confirmed the truck was still in the Park position. Truck had to be towed out of a ditch in the woods. I sustained moderate injuries, but thankfully was not catastrophically disabled. This should be investigated thoroughly, so that no other person(s) is injured or dies as a result of this defect.