Who's at-fault in this type of auto crash?

A mans car breaks down about 30 miles from home. Being short on cash, he calls his neighbor to come and help tow his vehicle home. The law states you cannot tow another vehicle, unless both vehicles are connected with a metal tow bar. Neighbor did not have a metal tow bar, but instead takes a 20 foot heavy-duty rope. Both vehicles are attached to the tow rope and they take off for home. Neighbor is in his vehicle and man is in his vehicle. engine is running in towed vehicle, in order to use the brakes and flashers. Neighbors vehicle has to make a sudden stop, on the road, and towed vehicle collides into the rear end of neighbors vehicle. No injuries. Substantial damages have occured to both vehicles. The police are called. Question: is this crash considered an auto accident or something else? And, who is at-fault for the damages and why?