By that I refer to the tradition at Comrades ultra marathon in South Africa.
There, the race director gets out at the finish line (alternating each year between Durban and Pietermaritzburg), turning his back to the oncoming field of runners and fires a pistol in the air at exactly the 12 hour mark. Any runner who has not crossed that line by that point will not receive a finishers medal nor be acknowledged as having even completed/entered the fifty four mile race.
Do any American marathons do anything like this? Would any try or would it be a public relations nightmare because it seemed mean spirited?