The sports industry has discovered, somewhat late, that young women will buy tickets to events if you give them a reason to show up.

This insight, which might have occurred to someone sooner, has manifested in the form of Fourth Wing Night, a promotional phenomenon sweeping through professional sports with the quiet determination of a franchise seeking new revenue streams. "Fourth Wing," for those who have not been paying attention to the young-adult publishing market, is a fantasy novel by Rebecca Yarros about dragon riders at a military academy. It has sold more than 30 million copies worldwide, which is to say it has sold more copies than most sports teams have sold tickets in their entire existence.

The Boston Red Sox, which hosted what the team calls its biggest promotion of all time, sold just under 11,000 tickets for its Fourth Wing Night in September. Travis Pollio, the club's senior director of ticket strategy and promotions, said the idea came from the team's 30-person employee book club, which is apparently a thing the Red Sox have. "I was like, 'Oh my God, can I board this plane?'" Mr. Pollio recalled of the initial sales surge, in what may be the first time a ticket executive has worried about selling out too quickly.

The demographics tell a story that the industry has been slow to read. The Red Sox reported that 59 percent of Fourth Wing ticket purchasers were female, compared with 37 percent for other games. More than half were first-time buyers. Commerce platform FEVO, which has facilitated 29 of these events, reports that each activation draws roughly 2,500 to 3,000 ticket sales.

(One notes that professional sports have spent decades and billions trying to attract new audiences, and it turns out the answer was dragons.)

The author, Ms. Yarros, receives no compensation for the events, according to her website. The teams, meanwhile, have discovered that fans who travel internationally to attend book signings will also travel domestically to attend hockey games, provided you give them a themed crewneck and a sangria called "Sorrengail."

Jennifer Nevins, who has spent 30 years with the St. Louis Blues, said Fourth Wing Night is the top-selling theme night in franchise history. "My initial sweatshirt order was 2,000," she said, "and I had to double that."

The lesson, as always, is that sports will eventually notice a cultural phenomenon — usually around the time it has sold 30 million of something.

Original story published in sportsbusinessjournal.com: "Teams turn 'Fourth Wing' fantasy into real ticketing opportunities"