Thanks to readers Ethan and Robin for sharing this one! — Dan

When it comes to lucky numbers, the number seven is probably the most popular, at least in the United States. Don’t take my word for it. In 2024, Reader’s Digest reported that “Alex Bellos, a mathematician and writer for The Guardian, set out to find the world’s favorite number [with no upper bound] in a massive, public vote on his website—which received more than 44,000 votes,' and the number seven came in first, with 10% of the vote. That matches what NPR found on July 7, 2007 (fun, right?), when Stanford professor named Keith Devlin told the radio network “if you ask people to pick a number between one and 10, almost everybody picks the number seven.”

And when it comes to luck and numbers, professional athletes — and those who aspire to go pro — often buy into the mythic power of a uniform number. It’s not a coincidence that some of history’s finest pro athletes — Cristiano Ronaldo, Mickey Mantle, Barry Bonds, John Elway, Pete Maravich, Ray Bourque, and many, more — have chosen to wear number 7, maybe in hopes of getting a little extra luck on the field, court, or ice.

But until recently, not all athletes could do that. Which is what makes the picture above so unusual.

The guy pictured is Kon Knueppel, now a professional basketball player with the Charlotte Hornets. He’s a rookie, but expectations are high — he was the fourth overall pick in the 2025 NBA Draft and earned MVP honors in the NBA Summer League Championship just a few months ago. At Duke, where he played just one season before going pro, Knueppel set an unusual record: he became the first player in at least half a century to wear number 7.

After the 1957-1958 NCAA basketball season, the Association adopted a seemingly weird rule, eventually known as Rule 1, Section 22, Clause b(2). That rule dictated the uniform numbers available to players, as articulated below (via this pdf):

It may not be immediately obvious, but that set of numbers omits the digits 6, 7, 8, and 9. And there was a good reason for that: we only have five fingers on each hand — and when it comes to referring games, that digital limitation could result in ambiguity. The New York Times explained:

Because referees signal fouls to the scorer’s table using their hands — one hand for the tens digit, one for the ones — all digits had to be countable on one hand. For example, two fingers on the right hand and five on the left means #25. A five on the right and two on the left means #52. But there’s no easy way to signal a single-digit 7 that way.

The NBA didn’t adopt the same rule, though, which always made the NCAA’s reasoning a bit suspect. (Refs can, and do, use their voice to resolve any ambiguity, and frequently point to the offending player, regardless.) It took a very long time, but before the 2023-2024 NCAA season, the Association eliminated the ban on sixes, sevens, eights, and nines.

No Duke freshman took advantage of the rule change in that first season, but Knueppel did the year after, becoming the first player at Duke in more than 60 years to wear lucky number 7.

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Today’s Bonus fact: In 1985, Charlie Kerfeld made his debut as a Major League Baseball pitcher, wearing #37. It was an homage to his favorite player, Larry Christenson, who had previously worn the same number for the Philadelphia Phillies. That’s not unusual — players adopt the numbers of their idols all the time — but Kerfeld went a bit further with his obsession. Before the 1987 season, the Astros offered Kerfeld a $110,000 contract. He turned it down because the team had offered the same amount to another pitcher, Jim DeShaies, and Kerfeld wanted to be paid more. On March 1, 1987, the Astros and Kerfeld finally came to an agreement. As This Day in Baseball explained, Kerfield accepted “a one-year contract worth $110,037.37 and 37 boxes of orange Jell-O, planned to be used future pranks. The Houston reliever, who wears number 37, insisted he earned more than right-hander Jim DeShaies, and the reliever’s new deal [paid] him $37.37 more than his teammate.”

From the Archives: Numbers Racket: Want a uniform number that your teammate already has? Maybe you can buy it off them.

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And thanks! — Dan