Last week at Wrigley Field, in the first of a five-game series with the Cubs, the Cardinals' Yadier Molina sent first baseman Matt Carpenter from first to third on a two-out double. But as Carpenter was rounding the hot corner in hopes of heading home, he stopped suddenly and returned to third base. Kyle Schwarber had just fielded Molina’s hit against the ivy in left field, and Carpenter knew better than to test his mettle against Schwarber’s arm.

The catch was emblematic of a shift in the slugger's game: Schwarber is slowly gaining the respect of opposing teams for his defense. Three seasons ago, when Schwarber made his debut with the Cubs, his status as a defender was nebulous. When he was drafted in 2014, he was famously adamant about his desire to be a catcher, and for the majority of his time in the minors, he was.

Since his June 2015 debut, though, Schwarber has played catcher only sparingly. Instead, he's learned the job of left fielder. It hasn't been easy: His early defensive gaffes spawned internet jokes and cemented a pesky narrative that he would forever be a defensive liability—certainly nobody to cause worry for the likes of Matt Carpenter.

But so far in 2018, Schwarber has statistically been almost the reverse of his old self. According to Defensive Runs Saved (DRS), which measures the number of runs a player is credited with saving or costing his team compared to the average, Schwarber cost the Cubs nine runs in 2017. Through the All Star break this year, he has saved them five. And according to UZR/150, a flawed but decent attempt at holistically quantifying on a player’s defense, Schwarber has doubled in value from last year. In fact, he currently rates as the best outfielder in baseball.

One standout feature of Schwarber's defense this season has been his arm. He's dazzled with long throws from left field on several occasions, and if Carpenter is a barometer, the league is beginning to take notice.

“All I try to do is get to the ball and make a good throw, an accurate throw,” Schwarber told Chicago after Thursday's game. “I’m not out there trying to show off by any means.”

But ask the guys who share the outfield with Schwarber, and they’ll describe his left-field cannon with more hubris.

“Knowing the ability he has on defense," said center fielder Albert Almora Jr., "every time I see a runner going to second before he’s rounding first, I’m like, ‘He’s out.’"

Right fielder Jason Heyward, winner of five Gold Gloves and lauded for his long throws from right field, echoed Almora.

“You kind of hope people run on him because he’s coming up ready to throw, and he has a good sense of keeping the ball down when it’s do or die,” Heyward said.

Joe Maddon, Cubs manager for the entirety of Schwarber’s major league tenure, said that Schwarber has always had a good arm, but that his technique and aggressiveness is helping him showcase it. “There’s no timidity to his game whatsoever,” Maddon said.

Schwarber’s arm is just a cog in his larger game, though. Outfielders don’t go from costing their team runs to saving them just because they can throw. In truth, Schwarber’s defensive transformation involves a lot more.

For one, his physical metamorphosis has been key. Over the winter, Schwarber altered his physique in such a dramatic fashion that by the Cubs Convention in January, it was drawing headlines. His work went beyond simple weight loss: at the same time as he was dropping pounds, Schwarber was doing drills that aren’t usually a part of a player’s routine until spring training.

“The work that he did in the offseason agility-wise, quickness-wise, it began there,” Maddon said. “I think the better frame, the better ability to move, technique should improve.”

Indeed, Schwarber's angles and routes to the ball have gotten better, Maddon said. A lot of that Schwarber credits to working with Will Venable, who after spending 2017 as a special assistant to the team now coaches first base and works with the outfielders. Venable played most of his career with the Padres before retiring in 2016.

“As soon as I got the job, I reached out to all the outfielders," said Venable. "Kyle was right from the beginning adamant that he wanted to improve on his defense. He’s a baseball rat. From day one the guy has been grinding out there. The guys all do a great job, but he’s the one guy in spring training that was out there every day doing early work at a high level.”

Venable recalls one emblematic incident with Schwarber: When the Cubs opened this season in Miami, in the third inning of the very first game, Schwarber made a fielding error on a line drive. Venable said that as soon as he saw it happen, he knew he needed to tell his left fielder not to let the game speed up on him. But Schwarber beat him to it.

“That was my intention, to have that talk, and before I could even get those words out, he hit me with the same message and said, ‘I just need to slow down and keep the ball in front and just make the plays that are there for me to make.’"

And since then, Schwarber has not made another error all season.

Beyond his offseason work, plain old practice has a lot to do with Schwarber's transformation. Heyward said that the best teacher is getting out there and doing it, and his teammate agreed. “Experience helps,” Schwarber said. “The more reps you get, the better you’re going to be.”

All told, Schwarber is a fairly new outfielder. He spent 136 innings as a catcher before leaving the position, and a gruesome injury sidelined him for practically all of the 2016 season. This is really only his second year as a full-time outfielder, and as he's gaining experience in left, he says picking the brains of guys like Heyward and Almora Jr. has helped tremendously. “[It helps] being able to talk to those guys, talk about situations and see what their thought process is when they’re out there,” Schwarber said. “I talk to Albert and J-Hey all the time.”

Some positive affirmation has helped his confidence, too. “After he makes a throw to the infield and gets somebody out, all the outfielders are looking at him and giving him a thumbs up,” Almora said. “Even if he’s safe, we’re giving him positive reinforcement.”

On that play that kept Carpenter at third base last week, he never ended up scoring. The Cubs won 9 to 6 that day, and Schwarber's saved run proved pivotal to the game's momentum. Afterward, Maddon put his left fielder's growth simply: “You tell this guy he’s not good out there at something, he’s going to do something about it,” he said. “And he did.”