At the 2012 Olympics, Missy Franklin was America’s swimming darling. A 17-year-old phenom with a backstroke so smooth and fast that she seemed to be powered by motor rather than arms and legs, Franklin won four gold medals in the London Games—two individual medals in the 100-meter and 200-meter backstroke and two in relays. She was unstoppable, and from her perspective the next decade must’ve looked like still pool water, waiting to be churned.

Four years later, things look very different. On Monday night, the 21-year-old Franklin came in dead last in her 200-meter freestyle semifinal, missing by a wide margin a spot in the medal race. Franklin didn’t even qualify for the 100-meter backstroke at the U.S. trials and so far she isn’t a part of any relay teams, though she could nab a spot on the 4-by-200-meter freestyle team. On Thursday she’ll race in the 200-meter backstroke, but it’s not a sure thing that she’ll make Friday’s final.

The disparity between the 2012 Franklin and 2016 Franklin is too big to miss. John Meyer of the Denver Post, Franklin’s hometown paper, wrote:

America has never seen this Missy Franklin before, in or out of the pool: finishing last in her semifinal heat and failing to advance to the finals of the 200-meter freestyle, then sharing her heartache with red eyes and a voice cracking with emotion.

Both images were shocking Monday night, and the star of the London Olympics can no longer be in denial. Something’s missing in Missy. She appears not to know what it is, but she can no longer hide her concerns with smiles and trademark optimism.

Her sudden decline has generated speculation about what slowed the once-dominant swimmer. Mere aging seems unlikely; many swimmers continue to thrive well into their 20s. Life changes, such as two years of college at Berkeley, probably played some role, but college swimmers have long showed up big at the Olympics—just look at Indiana freshman Lilly King, who won gold in the 100-meter breaststroke on Monday night.*

There are other, more baroque theories. In a long profile of Franklin, Bleacher Report’s Greg Couch points to a familiar and easily pilloried culprit: the NCAA.

Four years happened, the years from childhood to adulthood. Justin Bieber happened. The Harlem Globetrotters happened. College happened. Major life decisions, minor life decisions, growth, body changes, homework, moving away from home, coaching changes, winning the college national championship, injuries. Berkeley happened, and moving back home and changing coaches again happened. And also the big one:

The NCAA happened. Yes, the NCAA happened big time, forcing Franklin to make a pro-or-college decision that no one should have to make. The NCAA continues to cling to its ancient, made-up idea of amateurism for college athletes, even while sports bring in billions of TV dollars. Even the Olympics allow pros now. But American college athletes aren’t allowed to cash in.

Couch makes a case that the pressure to comply with NCAA regulations took a toll on Franklin.

If your kid is, say, a musician, he can go to college on a scholarship and make money on the side playing music gigs. If your kid is America’s sweetheart for swimming, under the NCAA’s amateurism rules, she cannot go to college on scholarship and make money on the side with swimming gigs.

The decisions Franklin had to make only hurt her, pressured her.

Slowed her down?

You’ll never find me defending the NCAA’s labyrinth of insane and incomprehensible amateurism rules, but the notion here that Franklin was done in by paperwork seems a little far-fetched. Couch writes that Franklin was flooded with offers, invitations, and media requests from all over the world after the 2012 games. And because she wasn’t allowed an agent as an amateur, she and her family had to deal with the deluge themselves. Franklin’s mother, a physician, “handled it by taking time away from her practice for more than a year to answer all requests and to try to keep pressure away from her daughter. Missy believes that requests should be answered, even if the answer is ‘no, thank you.’ “

That’s annoying for Franklin’s mother, but not a convincing explanation of Franklin’s slide. Far more damning, to me, seems to be the split from her youth coach, Todd Schmitz, while she swam for Berkeley, and the changes in her training regimen as a collegiate swimmer. Franklin’s best stroke is backstroke, but, Couch writes, her college team had other strong backstroke swimmers and needed the world-class Franklin to race in other events. “She was not asked to swim the 200-meter backstroke in the NCAA championships,” he writes. “So that was time not spent training in her specialty.”

Franklin herself is unable to explain the drop-off. After her dismal finish in the 200-meter freestyle semifinal, she told the Associated Press that “the hardest part is I wish I could understand and I wish I could fix it.” She went on: “But that’s kind of how my year has gone. I feel like I’ve worked as hard as I ever have and it just hasn’t been there.”

Back in June, during the U.S. trials in Omaha, Nebraska, there were questions about Franklin even making the Olympic team. The Washington Post’s Dave Sheinin wondered, “What is wrong with Franklin?” Like Couch, Sheinin points to causes beyond the pool: photo shoots, commercials, appearances along with training. Franklin reunited with Schmitz after she left Berkeley; he called her demanding schedule, “not ideal,” according to the article. Sheinin writes that the relentlessly cheery Franklin even admitted she found her sponsor and media obligations “a little bit more tiring than I was expecting it to be.”

But maybe the most convincing explanation of all is tucked quietly into an appositive about halfway through the story:

She insists her back—which suffered a crippling bout of spasms at the 2014 Pan Pacific Championships—is fine. But it still flares up occasionally, and more glaringly, the injury is also an obvious line of demarcation in her career: She hasn’t been the same since it first happened, with no victories in major international meets and no personal bests since 2014.

The spasms were severe enough that Franklin couldn’t move for 45 minutes, per the Denver Post. “The scariest 45 minutes of my life,” she called them. She managed to swim anyway, scoring four medals, only one of them gold.

There’s probably no single answer to the question of what’s slowing down Missy Franklin. Four years after her splashy arrival, she is now held up as a cautionary tale about everything from the phony amateurism of the NCAA to the demanding professionalization of Olympic sports. Her motor has died and she’s no longer steering her story.

*Correction, Aug. 9, 2016: This post originally misspelled the name of the University of California–Berkeley.

See more of Slate’s Olympics coverage.