That is because what physicists see with their eyes seems to conflict with a fundamental property of motion known as the conservation of angular momentum. It states that the axis of a spinning object, such as the tight spiral of well-thrown football, will not change its orientation unless some force acts to twist it. It was not clear what force could be pushing the football’s nose down.

Worse, the most simplistic analysis would suggest that the onrush of air from below would nudge the nose of the football up, not down, and flip it backward. If that were true, a long beautiful pass would be an impossibility.

“That’s the paradox,” said Dr. Gay, a professor of physics at the University of Nebraska in Lincoln, home of the Cornhuskers. “I worked on it for 20 years, and I didn’t make much progress till I brought in two smart people to help me and, and we spent three years yelling at each other about it.”