When the timer chimed to begin Round 3, Andy Cruz stalked Rostyslav Sabadash behind a stiff jab.

Sabadash, taller and bulkier, edged backward. Cruz, a Cuban boxer who had won the lightweight gold medal at the Tokyo Olympics in 2021, popped him with two more long lefts.

Cruz is one of the most accomplished fighters ever to emerge from Cuba’s celebrated boxing program. Along with his Olympic gold, he has three amateur world titles and has twice won at the Pan American Games. But in mid-May, Cruz arrived in Northeast Philadelphia to learn how to box like a pro: He will make his professional debut in Detroit on July 15, in a 10-round bout against a rugged veteran named Juan Carlos Burgos.

Cruz snapped off two more jabs, and then a right cross. Cruz’s manager, Yolfri Sánchez, watched the sparring session from ringside. His head coach, Derek Ennis — nicknamed Bozy — perched on the apron. Sánchez hired Ennis to replace Cruz’s amateur habits with pro techniques: hitting with authority, staying in range, catching and countering punches.

Another Cruz right hand started a heated exchange of blows. Ennis reined in his gym’s new star.

“That’s not what you want to do,” Ennis said. “Somebody bigger than you, don’t stand there and bang with him. Be smart.”

Cruz’s boxing I.Q., along with his speed and timing, helped make him the boxer many observers consider the best Cuban of his generation. A falling out with Cuba’s boxing federation led him to leave the country last year, which made Cruz boxing’s hottest free agent — and its most intriguing prospect.

In May, Cruz signed a three-year deal with Matchroom Boxing that will guarantee him payment in the seven figures, and Cruz’s backers think he will dominate the talent-rich lightweight division by next summer. But professional success will depend on how well Cruz adapts, both to his new country and to a new version of a familiar sport.

“Training is fine, but I need to fight,” he said in Spanish after the sparring session. “I’m anxious. I’m eager. I like to work under pressure. That’s when you get the best out of me.”

Cruz speaks little English, and Ennis speaks even less Spanish. Sánchez translates, and so do their smartphones. But Cruz is fluent in pugilism. The boxing database BoxRec credits him with 140 amateur wins. He acted on Ennis’s advice immediately.

Pivot. Right cross. Uppercut.

Both punches connected.

“That’s it!” Sánchez shouted in Spanish.

Cruz first gained notice in the United States in July 2021, dancing in the ring to celebrate his Olympic gold medal while the silver medalist, Keyshawn Davis of the United States, grandstanded in front of a TV camera. The rapper Snoop Dogg and the comedian Kevin Hart parodied the moment for laughs in a widely viewed video clip, but boxing aficionados focused on the result.

Davis was a highly rated amateur and is currently a fast-rising lightweight prospect, and Cruz had outclassed him — and not for the first time. Cruz is 4-0 against Davis.

“I had never seen anything like it,” said Eddie Hearn, the chairman of Matchroom Sport. “I know it sounds cheesy, but it was like watching an artist draw a painting. I was mesmerized by the ease he beat the best amateurs in the world. I never really expected to sign him because you don’t really expect Cuban fighters to turn pro.”

Cruz had been slated to make his professional debut last May, under a novel partnership between Cuba’s boxing federation and Golden Ring Promotions, which is based in Mexico. Cuban boxers could rise through professional rankings, and the federation would receive a cut of their payouts. Boxers would remain eligible for international competitions.

The arrangement was meant to showcase the whole Cuban team, but Cruz was the headliner. A video hyping his scheduled appearance remains on Golden Ring’s YouTube page.

But the day before the Cuban delegation traveled to Mexico, Cruz was dropped from the squad. In some accounts, officials cited a poor attitude and bad practice habits. But Cruz said the move had been pre-emptive, made by officials who were scared that he would abandon the team in Mexico.

In recent years Cuba’s once-mighty sports program has struggled to retain top-tier talent, with some athletes deserting national teams during trips abroad and others fleeing the country altogether. Several world-class athletes were among the more than a quarter million Cubans who migrated to the United States last year.

A javelin thrower, Yiselena Ballar Rojas, abandoned the national team last summer during a layover in Miami en route to the World Athletics Championships in Eugene, Ore. And Yaimé Pérez, the discus bronze medalist at the Tokyo Olympics, left the team in Miami after the World Championships.

And the boxer Yoenlis Hernández, the only Cuban to win gold at the world amateur championships in May, left the team on the way home from that tournament, slipping away during a stopover in Panama.

For his part, Cruz maintains that he would have stayed in Cuba if he hadn’t been excluded from the pro team.

“It disappointed me a lot,” said Cruz, who turns 28 in August. “I wanted to leave, whatever way I could.”

Last June, as part of a risky plot to leave Cuba by boat, Cruz traveled from his home in Matanzas, 65 miles east of Havana, to Moa, a seaside city in the eastern province of Holguín. He dozed off in the home of the man who organized the trip and awoke to police officers clamping handcuffs on him. After four days in custody, Cruz was allowed to return to Matanzas, but he was permanently removed from Cuba’s national team and banned from the country’s boxing gyms.

For the next four months, training meant shadowboxing and an hourlong run every afternoon. Cross-training meant playing pickup soccer. Without his monthly national team stipend — 10,000 Cuban pesos, or about $400 — Cruz ran low on money.

With no income, and pro boxing prospects looking remote, Cruz said he had considered selling peanuts for a living. At least then he could monetize his boxing success: If you’re choosing between vendors, why not buy from the Olympic champion?

“I was a little scared that my door to leave the country had closed, and it would cost me my career,” Cruz said. “Those six months in Cuba were hell, in the sense that I wasn’t doing what I’m most passionate about, what I like the most. That’s boxing.”

Speculation about Cruz’s future percolated all summer and eventually reached Sánchez, a baseball agent who is based in the Dominican Republic and who specializes in Cuban prospects. Sánchez wanted the boxer to be able to leave Cuba legally, and he worked with Cruz to arrange the necessary paperwork.

By last November, Cruz had a passport and a one-way plane ticket to Santo Domingo.

Cruz arrived on Nov. 5, 2022, wearing a white Stephen Curry jersey and a wide grin. He weighed 152 pounds, 17 above the 135-pound lightweight limit, but had shed some muscle since winning the Olympics.

“He was smaller than I had imagined,” Sánchez said. “I thought he’d be bigger.”

From there, Cruz’s lawyer in the United States worked on the visa Cruz would need to live and train in the country, while Sánchez and Jesse Rodriguez, his United States-based manager, negotiated with promoters. By early May, Cruz had secured both his visa and the promotional deal with Matchroom Boxing.

Cruz headed to Philadelphia, where he works with Ennis alongside the coach’s son, the welterweight contender Jaron Ennis — boxing most afternoons, working on strength and conditioning most nights. When he’s not training, Cruz often parks in front of the television in the extended-stay hotel room he shares with Sánchez and plays MLB The Show 23.

Cruz sent a new iPhone for his mom on a trip Rodriguez made to Cuba. Cruz asked Rodriguez to bring back his Olympic gold medal and a container of ground peanuts. He missed Cuban food, he said, but missed his family even more. The keepsakes would remind him of both.

“It’s the first time I’ve spent this much time so far from them,” he said of his parents, his brother and his 1-year-old son. “They were witnesses to everything that happened to me. They knew I didn’t have any other choice but to leave.”

Cruz spent the final four rounds of his sparring session schooling a local hopeful named Angel Pizarro. Cruz is leaner, stronger and 10 pounds lighter than when he left Cuba. After he landed a sharp jab and a hard right hand, Pizarro smiled and nodded to acknowledge Cruz’s new muscle.

“He a bully!” Pizarro shouted to the crowd around the ring.

Ennis said his goal was not to transform Cruz into a power puncher in the Mike Tyson mold, but to add pro-style strength to the speed and savvy that made Cruz a great amateur.

“I don’t take nothing away — I just add on, sharpen up and teach him my style,” Ennis said. “Catching the right hand, left hook. Rolling under shots, come back with the counter. That’s what I have him doing.”

For his part, Hearn said Cruz was already equipped to defeat the lightweight division’s elite, including Gervonta Davis, the ticket-selling knockout artist; Shakur Stevenson, the 2016 Olympic runner-up; and Devin Haney, the undisputed champion. A future matchup with Keyshawn Davis is a natural — the two have sniped at each other over social media since last spring.

But first up is Burgos, a hardened gatekeeper whose 35-7-3 record includes decision losses to Haney and Keyshawn Davis.

Where most professional debuts are scheduled for four or six rounds, Cruz’s fight against Burgos is contracted for 10. The bout’s length is evidence that promoters and regulators already consider Cruz a veteran.

And it signals that after several false starts, Cruz believes he can fast-track to the top of professional boxing.

“I want to win all my fights — win all the belts,” Cruz said. “I want to do what I did in amateur boxing. I had a great career, and I think I can repeat it.”