One of the wheels of a semi-truck was trapped in a hole. The truck's driver asked an on-site employee to hook the truck to a yard dog so they could pull the truck's wheel out of the hole. The on-site employee hooked the truck to the yard dog and then boarded and operated the yard dog. As the yard dog began pulling, the brakes on the yard dog malfunctioned, causing it to move backwards. The driver of the semi-truck was standing between the semi-truck and the yard dog, and was crushed between the vehicles, sustaining two broken hips and a crushed pelvis.