TOKYO — Isaiah Jewett wanted to show the world who he is, and he believed the place to do it would be the final of the men’s 800 meters. In the past three months, he had graduated from USC, won an NCAA championship and, with a bold move, pulled an upset to make the toughest team in the toughest race. On Sunday night, more than anything else, he wanted to place in the top two of his semifinal heat and make the Olympic final.

Coming around the final turn, he ran in a tightly bunched pack, in close pursuit of three runners. He felt confident in his race strategy and believed in his stamina. And then he felt something clip his foot. Jewett lost his balance and, in the biggest race of his life, tumbled to the ground. One portion of his Olympics had ended.

“It was devastating,” Jewett said.

There are athletes whose love for their sport radiates off them, and Jewett is one of those. He smiles on the start line. He races in sleek, black sunglasses. He hugs rivals at the finish line. In interviews, to describe his strategy or motivation, he often reaches for references to his beloved superhero anime — he watches a scene before every race. Even running the 800, the most grueling race, he relishes what he is doing. Each time he runs and discusses his race, it feels like an ode to the sport.

“It’s a whole concept of fighting,” Jewett said. “You’re learning things on the fly to get stronger and reach a new potential. I feel like track is like where you reach new potentials. You find your own superpower within the race. Whether it’s somebody that runs in the back or somebody that runs in the front or somebody that runs a part of the race differently, that’s their power. And it’s cool to test your power and abilities against somebody else. And getting stronger as a human being — that’s such a cool concept to me, that we can push our bodies and push our limits.”

Jewett had established a reputation as a front-runner. At the NCAA championships, he took an immediate lead and demolished the field. At the U.S. trials, Jewett burst off the line and panicked typically unflappable world champion Donavan Brazier. In the first round in Tokyo, he stormed to the front and maintained the lead on the second lap. Just as two opponents passed him and it appeared he had faded, he summoned enough to finish in 1:45.07, the fastest preliminary he had ever run.

“I realized my race strategy is what I am supposed to do to make me happy,” Jewett said Friday. “Having fun is so much a part of this. If you’re not having fun in the 800, you’re going to burn out really fast.”

Jewett’s coach, Quincy Watts, dislikes when people call him a front-runner. He believes Jewett can race in any style, from front or back. Before the semifinal, Jewett’s coach had told him the race would start fast and that he needed to conserve strength for a finishing kick.

“I’m feeling really good for a kick home,” Jewett told Watts before the race.

“Trust that,” the coach replied.

Jewett still felt confident as he neared the final stretch. He had wanted to stay outside to avoid traffic in a bunched race, but nearing the homestretch he had to move inside. As he prepared to kick, Jewett felt something hit the back of his heel. His right leg smacked into his left leg. He stumbled and collapsed to the brick-red track. His head thudded off the ground. Half of his body spilled on to the infield. Botswanan Nijel Amos, a veteran medal contender running right behind Jewett, tripped over him and crumpled next to him.

Once Jewett scraped himself off the track, he took a step toward Amos. Jewett leaned over and extended his hand. “Come on, man,” Jewett said. He pulled him to his feet.

“I’m sorry,” Amos said.

“Let’s just finish the race, man,” Jewett said.

Jewett and Amos put their arms around each other. They trotted slowly down the track, shoulder to shoulder, blood running down Jewett’s right leg.

“I knew if anything, just me, I always have to finish a race,” Jewett said.

When Jewett crossed the finish line with Amos, the clock showed 2:38.12. They had finished nearly a minute behind the winners, but they had finished.

“Regardless of how mad you are, you have to be a hero at the end of the day,” Jewett said. “That was my version of trying to be a hero, standing up and showing good character, even if it’s my rival or whoever I’m racing or if anything happened. I don’t want to show any bad blood, because that’s what heroes do. They show their humanity through who they are.”

Afterward, blood seeped on Jewett’s right leg. His head hurt where it had banged off the track. He felt hopeful officials would grant his protest and he could run in the final, but while Amos was later reinstated, Jewett was denied. He felt blessed to have competed in the Olympics.

“I felt like I had a really good chance of running into the final,” Jewett said. “That’s just super devastating because I felt like I was starting to show people who I am. I was going to show the world.”

He lost the opportunity to run Monday night. About one thing, Jewett was wrong. He did not make the 800-meter final, but the world knows who Isaiah Jewett is.