Was it just luck that kept people on the ground from being killed or injured in Dallas?

It was anything but luck. For decades, airshows have had federally mandated rules that prevent planes from flying over the crowds of people who are watching them fly. The catastrophic, mechanical failure-caused crash of a highly modified North American P-51 race plane into the crowd at Reno in which the pilot and ten spectators were killed---69 more spectators were injured---caused the FAA to tighten up the regulations further. The two planes that collided and crashed in Dallas were flying where they were supposed to flying. The real question is why one flew into the other.