The mysterious late caution period in Sunday's NASCAR Sprint Cup race at Bristol was the result of human error, according to series officials.
Carl Edwards was leading with three laps to go when the race went yellow, although the reason for the caution was unclear at the time.
Rain began to fall while the problem was being investigated, resulting in the race ending after 503 laps and Edwards declared the winner.
While the caution did not affect the outcome of the race, NASCAR vice president of competition and racing development Robin Pemberton said that it was "a stupid error".
"It appears that in the flag stand one of the flag people had leaned on the switch that is the manual override for the caution lights," he explained.
"At that time when the flag stand realised that the caution lights were illuminated, the flag man threw the flag, and then after that happened we froze the field from the [race control] tower.
"It appears that not all, but most, of the flag stands have a manual override for the caution lights, and due to the weather and due to other things, it wasn't secured properly, and the flag person leaned against the switch and turned the caution lights on.
"We tried to turn them off, and we realised that the override switch was on and they were hung on caution. It was a stupid error."
Pemberton added that the series will look into making changes that can prevent a repeat of the incident in the future.
"[For] all the electronics that we've had and have installed in the trailers for freezing the field and all these other things, you still have to integrate [them] into the track facilities," he said.
"There are probably some things that we needed to do to better secure that area where the manual override is on the lights."
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