In his fourth game as a major leaguer, 21-year-old Julio Rodríguez, the Seattle Mariners’ top prospect coming into the year, noticed the opposition was kind of sleeping on him. Specifically, Minnesota Twins pitcher Dylan Bundy and catcher Gary Sanchez had left him largely unchecked over at first after he walked. Probably they’d seen the scouting reports, which praised his control of the strike zone, ability to adjust and “plus-plus raw power,” while tempering expectations about his “average speed.”

One of a handful of top prospects who debuted on opening day this year, Rodríguez’s flashy tools took a few weeks to heat up. And at 6-foot-3, 228 pounds, he projected to be a bigger threat at the plate than on the basepaths.

Which is, frankly, part of why he opted to run. Because no one really expected him to — and because he was struggling to contribute in other ways — Rodríguez stole second, advancing to third on Sanchez’s errant throw.

That first one is still his favorite stolen base this season. There are now 11 to choose from, the most in Major League Baseball. Rodríguez knows he leads the league because people keep telling him about it, wondering with some incredulity how he got so fast.

“It’s just funny,” he says with a laugh, “‘cause before no one would have been talking about it.”

When he signed out of the Dominican Republic in 2017, scouts marveled that Rodriguez was “big for a 16-year-old and already getting bigger.” That translated to promising pop, but concerns that his middling speed would, if anything, decrease over time as he grew and matured. They pegged him as a corner outfield type, and even then he’d have to watch his body to stay effective in the field. The reports noted, however, that “Rodríguez takes pride in his defense.”

“Even though no scout will ever admit it,” says Mariners manager Scott Servais, “sometimes they’re wrong.”

Now, just over a month into his rookie season, Rodriguez not only leads baseball in steals, he’s in the top 2 percent of players for sprint speed. Only seven players, of several hundred, are faster. Recently, ahead of a game against the Mets in New York, he said that’s surprising to only the people who underestimated him.

Underestimated him? Or is it that he has gotten faster since then?

“Both. Before, I was definitely not the fastest runner, but I wasn't the runner people said that I was,” Rodríguez said. “Just got to put the work in and show them that they’re wrong. That was basically what I did.”

Learning to run

Ulises Cabrera, Rodríguez’s agent, thought those scouts were wrong. He thought Rodriguez could play center. Well, maybe if he was just a little faster.

So Cabrera asked Llewellyn “Yo” Murphy, a former football player who now runs a performance training facility in Tampa, Florida, whether Rodríguez could learn to run faster.

“I said he definitely can, not even a question,” Murphy says. “I won’t say he didn’t know how to run, because everyone knows how to run, but I just felt like he wasn’t maximizing what he had.”

In a post-Driveline world, independent trainers and programs have become mainstays in MLB athletes' lives. Specialized strength coaches and sports-science facilities offer the opportunity for players to fine tune every aspect of their game, which is what it takes to succeed at the highest level. Everything now is some sort of “lab.”

Murphy has worked with multiple clients of Cabrera’s, teaching them how to run correctly to maximize their athletic potential. About three years ago, he started working with Rodríguez, who, at 19, had a couple of goals.

“He wants to threaten people with his speed when he’s on base,” Murphy says. “He told me specifically he knew he could play center field and he wants to show that he can play that position.”

Murphy saw Rodríguez’s size as a tool — long levers and long strides — to be honed. The teen was taking short steps and spending too much time with his feet in the air. He needed to learn to hold his body at the right angle and attack the ground. They focused on acceleration, by pushing heavy sleds or pulling them and then removing the restraints, and just sprinting. But Rodríguez didn’t need to run the fastest 60-meter dash; he needed to be able to react to balls hit into the outfield and steal bases, so they ran practical drills, too, with actual baseball implications.

Early on in their time together, Murphy asked Rodríguez if he wanted to be great. It was meant to be a challenge.

“Julio has always worked hard for me,” Murphy says. “But I didn't see the purpose behind it, the intent behind it.”

Rodríguez — who fashioned himself “JRod” in homage to Alex Rodriguez and talked about how he wanted to “break baseball“ when he was just 17 and conducts all his interviews in English, despite it being his second language — wants to be great.

“I told him, you're the only one stopping yourself from being great,” Murphy says.

It was a tense conversation. It worked.

Finding a home in center field

Last year, in High-A, Rodríguez stole five bases in a month and a half. According to him, “people” said that was just because the experimental rules at that level limited pitchers’ pick-off attempts. Frustrated, he stopped running. Then he got promoted to Double-A, where there are no pick-off rules.

“That's when I started running again,” Rodríguez says, “and I stole like 15 or 16 bags in 40-something games.”

He alway had the eye and the acumen to steal bases, his newfound speed just unlocked an ability. In the offseason, Rodríguez went back to Murphy, the conversation about greatness still nagging at him. And this spring, when he reported to the big league camp, coaches noticed something different.

Servais says he’d be lying if he said he always thought Rodríguez had the speed necessary to be a center fielder.

“I didn't see it coming,” he says. “Until I got to spring training. It was one of the first days we ran the bases as a team, early camp, and the way he's flying around the base like, oh my God, this is different. And you start seeing him move in the outfield, and his ability to close on balls.”

Just before the end of spring training, Rodríguez emphatically legged out an inside-the-park home run, his sprint speed on full display. Three days later, he was told he made the opening day roster. The Mariners shared a video of Servais giving him the good news, it opens with the manager saying, “You look comfortable in center field.”

“I am,” Rodríguez says.

‘Huge, huge, huge upside’

Murphy says that even most top athletes could learn to run more correctly. They don’t bother because the ones who are fast don’t feel like they need to, and the ones who are slow would rather focus on their strengths.

Rodríguez is not like that.

“He has a huge, huge, huge upside,” Murphy says. “And one reason is his humility; he really focuses on what he’s not good at.”

That humility is evident in his dedication to training, his approachability, and, of course, the results. But Rodríguez — who sits on the floor of the visiting team clubhouse eating Froot Loops and says going up against guys like Max Scherzer used to seem like a daunting challenge only now he’s basically used to the big leagues — is made up of at least as much confidence as modesty.

“I feel like this is the year that everything actually took off, and people see what they thought was not gonna even be possible,” he says. “So joke's on them.”