YOKOHAMA, Japan — As competition got underway in Tokyo, only 142 athletes in the history of the Games had competed in both the Summer and Winter Olympics. That group is small for obvious reasons. It’s really hard to do.

But when he dug into the batter’s box on Friday night at Yokohama Baseball Stadium, Eddy Alvarez, a member of the United States' team, joined the club.

At the Winter Games in Sochi in 2014, Alvarez, a Miami native who used to perform tricks on roller skates in South Beach as a young boy, won a silver medal as part of the United States’ 5,000-meter relay team in short-track speedskating. At the Tokyo Olympics, where baseball has returned to the Summer Games for the first time since 2008, he is the U.S. team’s starting second baseman.

The similarities between the sports? “Turning left,” Alvarez, 31, said recently with a chuckle. “That’s it.”

Alvarez, though, is trying for an even higher degree of difficulty: to become just the sixth person ever to win a medal in both the Summer and Winter Games.

The only Americans to have achieved this are Eddie Eagan (boxing gold in 1920 and bobsled gold in 1932) and Lauryn Williams (track silver in 2004, track gold in 2012 and bobsled silver in 2014). And with the United States’ baseball team considered the best challenger to top-ranked Japan, Alvarez has a good shot at joining them.

“I’m not saying I am the greatest athlete ever to walk this planet, but to be in that elite group is something special,” he said, adding, “just to be that small percentage of that small percentage is nuts.”

Watch Alvarez play now and it is clear how he managed to pull this off. On a field with other top athletes, he is faster and more graceful, darting around the infield or bases with little wasted movement. But that athleticism has also been accompanied by a lifetime tug of war between skating and baseball.

At 4, he got his first pair of skates for Christmas. By 6, he had picked up tricks from older skaters at the beach and caught enough people’s eye that a local skate store asked to sponsor him. By 11, he had won youth national titles in in-line, long- and short-track speedskating in the same year and earned the nickname Eddy “The Jet.”

“He has always been so freaking coordinated,” his father, Walter Alvarez, said. “It was like a thing of beauty to see him on the ice.”

Baseball, though, was expected to be Alvarez’s main sport, much like his older brother, Nick, 44, who spent seven years in the minor leagues of the Los Angeles Dodgers organization. And the sport, of course, is immensely popular in Cuba, where his parents are from, and among Latinos in South Florida.

But Alvarez kept demonstrating such aptitude on his feet that he transitioned to in-line speedskating and then the ice. At an in-line skating center in Miami, he met a trailblazer who inspired him and his family to keep going: Jennifer Rodriguez, the first Cuban American to participate in the Winter Games (the 1996 Nagano Olympics) and the first to win a medal (two bronzes in long track speedskating at the 2002 Salt Lake City Games).

“He was really small, but he was super fast,” said Rodriguez, 45, about practicing with a young Alvarez. “To be honest, he was this little irritating guy. I couldn’t drop him. He was right on our tail.”

After juggling both disciplines for so long, squeezing in naps and homework while his parents ferried him to the next practice or competition, Alvarez decided while attending Christopher Columbus High in Miami, a baseball powerhouse, that it was time to get serious about one. He felt he had surpassed all expectations as a skater so he chose what he called his true passion: baseball.

Alvarez said he never intended to continue bouncing between the sports, but it kept happening. When a small college was the only one to offer him a full athletic scholarship because he was undersized, he refocused on his Olympic dream.

Back and forth it went. After he didn’t qualify for the 2010 Games, he gave baseball another shot. He made it onto the Salt Lake City Community College baseball team as a walk-on in 2011 and overcame double knee surgery to earn a spot at the 2014 Games in Sochi, Russia.

“Not a day goes by that I don’t remember my experience at the Olympics,” he said, including the stumbles.

In three individual races, Alvarez either slipped, was knocked down or was disqualified. But his 5,000-meter relay team reached the final. The U.S. lost to Russia by less than three-tenths of a second.

Losing to athletes from a federation since found to have participated in the most elaborate doping program in sports history still bugs Alvarez. Three members of the Russian squad that beat Alvarez’s team — including Viktor Ahn, the most decorated Olympic short-track speedskater in history — were among the dozens of athletes barred from the 2018 Games.

“We just kind of feel cheated,” Alvarez said, calling the Tokyo Olympics “a true second chance.”

No matter the outcome of those Winter Games, though, Alvarez said he had already made up his mind beforehand: he was going back to baseball — again — even though many, his father included, were hoping he would return in four years for a shot at a gold medal in speedskating.

“If I wanted to be a professional baseball player at some point, I knew I would have to do the jump ASAP because unfortunately age is a huge factor,” said Alvarez, whose backup plan was skating.

Alvarez began overhauling his 5-foot-9, 150-pound frame from a physique beneficial for speedskating, with a muscular lower body and skinny arms, to one with upper body strength and mass to swing a bat with force.

Teams had little interest in an athletic but rusty 24-year-old. But after watching Alvarez work out, the Chicago White Sox called — the first club to do so — and he immediately signed a minor-league contract, a mere four months after his final race in Sochi.

After a promising start, Alvarez struggled. Inching toward 30 and still in the minor leagues, he was traded to his hometown Marlins in 2019. He had his best season yet.

And in 2020, after a coronavirus outbreak debilitated the Marlins roster, Alvarez made his major-league debut. Even though he sputtered and hit .189 in 12 games, he believes his seasoning helped him land an invitation from the U.S. national team for qualifiers in June.

With Alvarez’s speed and bat, the United States earned a spot in the Olympics. He was chosen, along with the W.N.B.A. star Sue Bird, to serve as a flag bearer for the Americans at the opening ceremony. On the field, he has remained the team’s sparkplug.

Watching from afar, Rodriguez has marveled at how the little skater from Miami who became a silver medalist has reached the highest levels of another sport, one so different and dependent on hand-eye coordination.

“The technique in baseball is night and day different from skating, which is a lot of strength and stamina,” she said. “You put me on the baseball field and it doesn’t work. I can’t play tennis. I can’t do anything that’s hand-eye coordinated. It looks awful.”

The last time Alvarez was at the Olympics, he said he was so overwhelmed trying to soak up the experience that it was hard to concentrate at times. Seven years later, Alvarez said he feels more comfortable, a change he hopes will help him avoid having to hear another country’s national anthem played when the gold medals are presented again.

“This feels like a redemption trip for me,” he said.