Updated September 17, 2023 at 4:18 PM ET

American rider Sepp Kuss has won La Vuelta a España, one of cycling's crown jewels, turning the crowd favorite into a surprise champion.

"I think I'll just look back on this experience with a lot of fond memories," Kuss said in an interview after his victory. "It's still sinking in. I think that's gonna take quite some time."

But in a dramatic twist, the biggest threat to Kuss during the three-week race came from within his own team — including a much-criticized attack on Kuss' birthday that cut into his lead.

The result was an international sports controversy with all the trimmings, one that gets to the heart of how elite road cycling defines itself in its most high-profile team events.

Here's a quick guide to what's been going on in Spain:

Kuss is on cycling's most dominant team

Kuss' teammates on the Jumbo-Visma squad included two of the top cyclists in recent memory: two-time Tour de France winner Jonas Vingegaard and three-time Vuelta champion Primož Roglič (who also won this year's Giro d'Italia).

Kuss, who is from Durango, Colo., faithfully served both Vingegaard and Roglič in key moments, pacing them on brutal climbs, shielding them from the wind and chasing down their rivals. By being a loyal domestique, or support rider, he repeatedly helped them climb to the top of the podium.

On Friday, the trio was ranked 1-2-3 in La Vuelta, nearly three minutes ahead of their closest rival. On its face, that's a bit boring. But in a fascinating twist, it's Kuss who had been wearing La Roja — the Spanish equivalent of the French yellow jersey — since becoming the race's leader on Sept. 2.

There's just one snag: Kuss was not the leader of Jumbo-Visma.

Ander Gillenea / AFP via Getty Images

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AFP via Getty Images

With the team in control in La Vuelta's final week, Jumbo-Visma had been under intense public scrutiny: Would the squad and its elite competitors allow Kuss to keep the famed red jersey all the way to Madrid?

On one side are those who say Kuss, a well-liked "super domestique" who has been integral to the world-beating successes of Team Jumbo-Visma, earned the right to vie for a Grand Tour victory of his own.

On the other side are those who say that the whole point of stage races such as La Vuelta and the Tour de France is to sort out the top cyclists, after thousands of miles and daunting climbs.

The birthday surprise, and an epic backlash

It was all smiles at the start of Wednesday's stage, when Kuss was presented with a cake and serenaded with "Cumpleaños Feliz" in honor of his 29th birthday. But by the end of the day, cycling fans were hotly accusing Kuss' teammates of betrayal.

Roglič attacked late in the race, sprinting ahead of a handful of riders up the storied heights of the Alto de l'Angliru in the Asturias mountains, where the road soars up inclines of 20% in some spots. Only Vingegaard and Kuss were able to reunite with Roglič — and in a stunning moment, when Kuss faltered, his teammates simply dropped him, pedaling away into the mist.

The pair sliced 19 seconds off of Kuss' advantage, leaving Vingegaard just 8 seconds behind. They were also condemned for essentially attacking their teammate while he was wearing the race leader's jersey.

"It was a much nicer result than last time," Roglič said, referring to 2020, when he lost the red jersey on the Angliru. But as many fans quickly noted, that year's punishing stage was one in which Kuss stayed with his teammate and helped him limit the damage.

Suspicions of an intra-team battle had risen one day earlier, when Vingegaard mounted an attack on the final climb that put him just 29 seconds behind Kuss and brought the Dane his second stage win.

"I don't know if I'll take the overall lead tomorrow," Vingegaard said at the time, reassuring no one.

When "tomorrow" came, there was Vingegaard, following Roglič's wheel to take more time out of Kuss. Compared to his actions, his comments afterward were hard to parse.

"To be honest, I actually hope that [Kuss] will keep the jersey," he said. "I would love to see Sepp winning this Vuelta a Espana." On Instagram and elsewhere, the Dane dedicated his win to an injured teammate. But cycling fans were incensed, criticizing Vingegaard and Roglič for dropping a teammate who was wearing the leader's jersey.

A public debate explodes

In a three-week stage race, it's not rare for a race leader to have an off day. But for many cycling fans, it was stunning to see Kuss' teammates abandon him, after the three had left all the other riders behind — both on the day's stage and in the overall standings.

Veteran cyclists also noted the rarity of the moment.

"There shouldn't be any gifts in a grand tour win," former Tour de France winner Geraint Thomas said. But he added that in his view, Kuss has proven he's good enough to earn the win in Spain.

"So yeah, I feel for Kuss. I feel like he deserves a bit more respect," veteran rider Geraint Thomas said. "Not necessarily from the riders, either. I think more from the team. I think the team should be stronger with that."

Thomas later added, "Obviously, I would love to see Sepp win. And I think most of the peloton would, as well."

The uproar quieted on Thursday, when Roglič and Vingegaard shepherded Kuss through one of the final stages standing between him and the title. They even led him out to the finish, letting Kuss sprint ahead to defuse any challenges.

"It's an honor to have two such champions working for you," Kuss said afterward, noting his teammates' recent wins. He also praised the local fans: "It's probably the best part of being a professional cyclist. You feel the passion and the emotion when people cheer you on from the sidelines. It touches me every time."

Kuss also said his team has a plan — and Vingegaard affirmed the aim to defend Kuss' lead.

"We are in an excellent position, but we are not there yet," he said. "Saturday's stage is treacherous. It's fantastic to be able to do something for Sepp in this way. I will always remember what he has done for me. So, I wanted to give something back. Hopefully, we can bring his red jersey to the finish line."

The crowds in Spain chant: "Kuss! Kuss!"

Sepp Kuss had already endeared himself to cycling fans for taking on the sport's most painful assignments without complaint, grinding his team's rivals down as he dragged his leaders up the sides of mountains and literally carried their water.

Increasingly, that affection has blossomed into full-bore love, as evidenced by the crowd of fans who cheerfully mobbed Kuss as he left — or attempted to leave — his hotel Friday morning.

For signs of what makes this American so appealing, watch his actions. Here's Kuss answering reporters' questions in Spanish; there's Kuss jumping out of the front seat of a team car, offering it to Roglič (who declined). Here's Kuss apologizing for sprinting for third place, saying he needed the bonus seconds to retain La Roja.

And there's Kuss chugging champagne, or admitting this week that he was surprised to learn he was still leading the race — and with a smile on his face, refusing to attack his teammates.

His humility and modesty, paired with his obvious talents, have made him an eminently likable American in Europe — so much so that Europeans turned on their own this week, to cheer for the "Durango Kid" to win it all.

Even before this week's high drama, fans of Kuss mounted a "GC Kuss" campaign, saying he should ride for "general classification," seeking the overall win in multistage races, rather than sacrificing himself for others. For one race, at least, that wish is being fulfilled.

NPR's Joe Hernandez contributed to this story.

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