MESA, Ariz. -- As talk persists about potentially bringing the designated hitter to the National League at some point in the near future, Cubs fans naturally think of Kyle Schwarber. His days as a catcher did not last long in the Majors, and doubts existed as to whether he could make a successful transition to left field.

"Just tell Schwarbs he can't do something," Cubs manager Joe Maddon said, "and then just stay out of his way."

A year ago, Schwarber stunned the baseball world when he arrived to Cubs camp noticeably slimmed down in an effort to improve his mobility as an outfielder. The physical changes did not impact his power in the batter's box and helped him turn the page on the defensive struggles of the previous campaign.

This spring, Schwarber now has an even stronger defensive base as he works to fine-tune aspects of his game as the Cubs' primary left fielder. Depending on what metrics you pore through, there were still mixed results from him in the field in 2018. But there is no denying that Schwarber made an incredible leap from '17 and made Chicago more comfortable with keeping him entrenched in the corner.

"He did a great job out there," said Cubs first-base coach Will Venable, who works with the outfielders. "And he really progressed and accomplished a lot of things that he wanted to accomplish in Spring Training. He went out and did it and got positive results. The foundation is set. He's got confidence. Now it's just about continuing to build and continuing to work."

Looking at Outs Above Average via Statcast, Schwarber checks in at minus eight for 2018 (minus two on balls back and minus six on balls in). While single-season advanced statistics for defense still leave plenty of margin for error, there were strides made in a number of other notable categories. Schwarber had two Defensive Runs Saved, compared to minus nine in '17, for example.

Per Fangraphs, Schwarber's 4.9 Defensive Runs Above Average were the second highest total among 13 qualified left fielders. His 7.9 Arm Runs Above Average ranked first, and the 14 Ultimate Zone Rating that Schwarber posted ranked him second, among that same group. According to Inside Edge, Schwarber made 71.4 percent of "likely" plays, up from 54.5 percent in '17.

"He worked really hard," Maddon said. "He got his body in much better shape. He moved more efficiently. He got really, a lot better at going back on angles. The left fielder doesn't normally have a chance to go straight back. That's more of a center fielder's kind of a domain. But the corner guy's got a chance to work on angles. Steep angles. And I thought he did a really good job with that.

"Charging the ball and throwing it, [he was] one of the better ones actually last year. He just works."

Schwarber cited route efficiency and going back on balls -- especially being able to take his eyes off a ball in flight to get to a spot faster -- as an area he needs to concentrate on this spring. He also noted that he continues to pick the brains of the other Cubs outfielders.

"I take a lot of pride in my defense," Schwarber said. "I want to be good at what I do, and now being a full-time outfielder, that's my job. I just want to be able to take in as much information as I can."

And maybe he can stave off some DH talk in the process.

"I want to be a National League player for as long as I can be," Schwarber said. "I'd love to be a Chicago Cub for the rest of my career. And if it does come in, it comes in. But I'm just going to keep working on my craft out there."