How did Papa's leg get broken ?

A truck with its lights off approached them from behind, and they didn't hear it because of the storm. It suddenly turned on its lights, Papa grabbed his shotgun, and someone in the truck shot Papa, grazing his temple. The horse reared up and the wagon rolled over Papa's leg. Papa told Stacey to hide in the gully. The men shot at and missed Mr. Morrison, who threw one of them to the ground and fought with the other two. Badly injured, the men drove off. Mr. Morrison put the wheel on and they came home.

There cart ran it over.