Emily Calhoun remembers the moment she realized her worlds were colliding. It was in the early days of the 2023 N.F.L. season, and suddenly her phone was buzzing nonstop.

“Twelve people called me,” she said. “‘Are you seeing this?!’”

Ms. Calhoun, who was raised on Denver Broncos football, sure was. It was impossible to miss the seismic overlap. Her love of football was fusing with her fandom of another pop culture phenomenon: a onetime country singer whom Ms. Calhoun, 38, had come to love in the early 2000s.

We’re talking, of course, about one of the most consequential mergers of our time, one that united two of the world’s most rabid fan bases in unholy internet matrimony: Taylor Swift and the N.F.L., via her boyfriend, Kansas City Chiefs tight end Travis Kelce.

For the sliver of fans like Ms. Calhoun, it’s been a joyful, and complicated, overlap of identities and algorithms. They have been in fantasy drafts and in the Ticketmaster queues. They’re in the same stadiums for the Eras Tour as they are on a Sunday in September. They’re probably even in your football groupchats, the middle section of the Venn diagram that has animated American sports for the last year: Swifties who grew up football die-hards.

“It was like two elemental forces that shouldn’t be allowed to touch,” Prof. Galen Clavio, who studies sports and social media at Indiana University, said of the collision.

In the months since the Swift-Kelce relationship started, a considerable amount of ink has been spilled on the dynamics of their romance. There was the outrage over the pop star supposedly usurping substantial camera time during N.F.L. broadcasts (she really wasn’t), the navel-gazing over whether the relationship was a publicity stunt, and then, finally, the spiral into conspiracy, with some right-wing commenters speculating that the relationship was somehow a scheme to support President Biden in the 2024 election.

Lost in the coverage, though, were the crossover fans who for years have loved both sides of the Kelce-Swift union. It’s a bigger contingent than one might think, and it may have borne the most complicated and acute burden throughout the saga.

Some are wary of their worlds colliding. Others resent having become the reluctant mediator between friends and family in either camp. Still others are thrilled that their distinct identities are now catered to by a single algorithm.

“I couldn’t get enough of the content. I still am not sick of it,” said Sarah Taylor, 35, a lifelong Philadelphia Eagles fan who saw Ms. Swift’s Reputation and 1989 tours at Lincoln Financial Field — the same stadium where she has seen the Eagles play.

In Swiftie lore, the N.F.L. has been trying to harness the full power of Ms. Swift, who has famously turned down requests to perform at the Super Bowl. Such long-running commercial plays have made even some football-inclined Taylor fans skeptical of the N.F.L.’s focus on the pop star. The Swift references during broadcasts seemed more like pandering, bound to frustrate football fans.

Rochelle Hovde, 25, was raised in a Minnesota Vikings family. Even as a longtime Swiftie — Mx. Hovde, who uses they/them pronouns, recently saw the Eras tour — they grew frustrated with the way Taylor mania seeped into postgame interviews.

“I love talking about Taylor, but I also watch the interviews to listen to the players talk about the game,” Mx. Hovde said. They occasionally had to navigate family comments about Ms. Swift, or football naïveté from Swiftie friends, but otherwise relished bringing the two worlds together. They even hosted a Swift-themed Super Bowl party.

Crossover challenges are faced, usually on a smaller scale, whenever online groups intersect, especially when those communities have their own language and codes.

“You might send a message with the Taylor Swift audience in mind, and now you’re getting that message viewed with a bunch of Chiefs fans,” said William Brady, a professor of psychology who studies social networks and group behavior at Northwestern University.

Darker, more existential possibilities may arise if the couple calls it quits, though. Plenty of celebrity romances have come and gone in the N.F.L., but few have had the animating power of Ms. Swift, whose disciples have historically turned on her former paramours. That’s tougher to do if Mr. Kelce and his Chiefs define your Sundays.

Jennifer Barbour, a longtime Chiefs fan, has no intention of picking sides should that occur. “They’re not my friends. I don’t have to,” she said. But, she added, if they do split, “I’ll be interested to hear her love story and breakup albums about him.”

Perhaps the best that crossover fans can hope for if the Taylor-Travis romance is to end, Professor Clavio said, is that the pair will have the decency to do it like most consequential football decouplings: secretly, suddenly, and during the offseason.

Largely, though, the Swiftie football lovers are enjoying the influx of new fans. Ms. Calhoun saw the transformation in real time in her women-only fantasy league. The group had been going for 12 years, she said, and included a token friend who knew nothing about football and just played for fun, drafting players based on their looks.

Until this season, when the woman in question surprised them all by casually dropping player stats and trade news into the conversation.

“Oh my God,” Ms. Calhoun remembered saying, thrilled. “You’re a football fan now!”