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RIO DE JANEIRO – When Jahvid Best learned earlier this year that he would represent St. Lucia at the Olympics in the 100 meters, the former NFL running back had only one request.

He wanted to run against Usain Bolt.

“I told everyone I pray I’m in his heat,” Best said. “My prayers got answered.”

Even though Best finished more than three-tenths of a second behind Bolt and failed to advance to Sunday’s 100-meter semifinals, that hardly dampened his enthusiasm. He was thrilled to have the chance to compete at the Olympics at all considering he has run only about eight races since deciding last year to pursue sprinting as a second act in his athletic career.

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“What I’m using this for is just experience,” Best said. “This is the first time I’ve ever run in front of a crowd of more than 500 people at a track event. It’s just a blessing for me. I’m looking forward to a bright future in track and field. I know I can master this sport just like I did football.”

Best appeared in 22 games in two seasons with the Detroit Lions and made 15 starts, but concussions cut short the former first-round pick’s promising career. Doctors never again medically cleared him to play football after he suffered his second concussion of the 2011 season when he endured a big hit against the 49ers and the back of his head hit the turf hard.

When the Lions released him in July 2013, Best returned to his alma mater Cal to take classes and help out the football team. That kept Best occupied for the next year, but it did not satisfy his desire to challenge himself athletically.

“I was just losing my competitive edge,” Best said. “I had a need to compete. I said, ‘Let me just go run in open track meets just so I can compete against people.’ ”

Best had shown promise as a sprinter at Salesian High School in Richmond, Calif. He finished fifth in the 100 (10.31 seconds) and second in the 200 (20.65) at the 2007 California State meet, but he had not run a single race since deciding to focus exclusively on football at Cal.

The first few events Best entered last year were unsanctioned open races in California or Arizona. He enjoyed enough success that he moved to Arizona to join former Olympic gold medalist Maurice Greene’s training group.

Since Best would have to run a sub-10-second 100 meters to have any hope of making the U.S. team at a major meet, he chose to represent his father’s native St. Lucia instead. He qualified for the Olympics in April when he ran a personal-best 10.16 seconds at a small meet in San Diego.

When Best walked out onto the track at Olympic Stadium for Saturday’s seventh 100-meter heat, the polite applause he received was dwarfed by the thunderous roar for Bolt. Few in the crowd knew or cared that Best had set Cal’s school record for rushing yards in a game or that he was averaging 4.6 yards per carry for the Lions when he suffered his final concussion.

“The only time I really noticed [Bolt] was at the start when everybody was cheering for him,” Best said. “I just pretended they were cheering for me instead.”

The Olympics arrived too soon for Best to have any real hope of advancing out of the preliminary rounds. He finished seventh in his heat at 10.39 seconds, no surprise considering he’s still fine-tuning his start and his drive phase and seeking to shed his excess football weight.

But Best, 27, takes solace in seeing 34-year-old American Justin Gatlin still contending for medals at the Olympics and the World Championships. He believes he has that sort of potential, too, if he dedicates himself to track the way he once did to football.

“This is only my second year running,” Best said. “I ran this race as a kid, and I know I can master this sport. It’s just going to take time to shake all this rust off.”

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