Thanks to Statcast and other player tracking systems, we better understand defense now more than at any other point in baseball history. That doesn't mean we know everything, of course. Competing defensive metrics can tell us different things about the same player, and the eye test still matters too. You just have to know what you're looking at.

Last week we looked at how three pitchers could perform with their new catchers. This week we're going to examine three position players who showed much improved defense in 2019, and whether it could be sustainable going forward. Like batting average, defense can vary wildly from year-to-year, but sometimes a hot streak is an indication of legitimate improvement.

Mitch Garver
MIN • C • 8
2019 stats
View Profile

"It's the only reason I'm still catching, really," Twins catcher Mitch Garver told FiveThirtyEight's Travis Sawchik last September. Garver was referring to a new one-knee catching stance former Twins catching coach Tanner Swanson helped him adopt last year. The adjustment allowed Garver to improve his pitch-framing without sacrificing his blocking ability.

Specifically, the one-knee stance helped Garver better frame low pitches. In 2017, he turned pitches at the bottom of the zone into a called strike only 25 percent of the time. His overall called strike rate was near the bottom of the league at 42 percent. Last year Garver improved to 48.2 percent called strikes, among the best in baseball, including 41 percent at the bottom of the zone.

Here are the before and after GIFs. On the left is Garver poorly framing a curveball at the knees in 2018. On the right is Garver framing a nearly identical pitch for a called strike in 2019. The one-knee stance puts him in a much more athletic position, allowing him to more smoothly receive the ball. Framing is all about presentation and Garver's presentation is much improved.

In 2019, Mitch Garver adopted a one-knee stance that helped him frame low pitches. Sports

"A lot of times with those big-depth breaking balls, those sliders that sweep across the front of the zone, they go in and out of the zone," Garver told Sawchik. "They are very hard to catch. You have to learn how to catch them properly. I wanted to get underneath the ball when I'm receiving it." 

Garver went from minus-8.2 framing runs in 2018 to plus-4.2 framing runs in 2019, which qualifies as substantial improvement. He did that while maintaining his league-average blocking ability:

  • 2018: plus-0.2 blocking runs and one passed ball every 20.3 innings
  • 2019: minus-0.3 blocking runs and one passed ball every 22.5 innings

Of course, defense is secondary with Garver. He slugged 31 home runs in only 359 plate appearances last season -- Garver was the first catcher other than Gary Sanchez* to hit 30 homers in a season since Mike Napoli hit 30 with the 2011 Rangers -- so he's an offensive force at the position. With the improved defense, he's suddenly one of the best all-around catchers in the sport.

* The Yankees were so impressed by Garver's improvement that they hired Swanson away from the Twins over the winter so he could work his magic with Sanchez. You know you've done something right when a smart team swoops in to hire your coaches.

Bryce Harper
PHI • RF • 3
2019 stats
View Profile

About 16 months ago, Bryce Harper's defensive decline was a major talking point during his ongoing free agency. Harper consistently rated as an average or better defender from 2013-17, but his numbers went in the tank in 2018. He went from minus-2 runs saved defensively in 2017 -- more or less league average given the error bars in the data -- to minus-16.2 runs in 2018.

Only one player saw a bigger defensive decline from 2017 to 2018:

  1. Odubel Herrera: -18.5 runs (plus-9.6 to minus-9.0)
  2. Bryce Harper: -16.2 runs (minus-2.0 to minus-18.1)
  3. Evan Gattis: -15.8 runs (plus-3.9 to minus-11.8)
  4. Dee Gordon: -15.8 runs (plus-9.8 to minus-5.9)
  5. Tucker Barnhart: -14.2 runs (plus-5.2 to minus-8.9)

A one-year sample of defensive numbers should always be taken with a grain of salt. In Harper's case, he was already a polarizing player, and he was looking for a record-breaking contract, so any flaw in his game was going to be picked apart. His defensive numbers went from consistently solid to suddenly terrible. It was a red flag at the very least.

"I know I was terrible last year in center field. I feel like if I can stay out of center field, that'd be great," Harper told reporters, including NBC Sports Philadelphia's Corey Seidman, about his defense last spring. "... I think it was more of playing about 65 (games) in center field. That takes a toll on myself I guess, but it's no excuse. For me, it's just getting better out there. My knees felt great. Not making those overthrows, really making the right decisions."

Last offseason's Mike Petriello wrote a great breakdown of Harper's defensive issues. Long story short, his positioning wasn't great, and there were times he appeared passive in the field. It was easy to watch some highlights and think Harper was playing cautiously to avoid a major injury in his free agency season. He wasn't going all out, all the time.

The defensive decline appears to have been a one-year blip. Harper rebounded to plus-3.0 runs saved defensively with the Phillies last season, so more or less league average again. The 21.2-run improvement from 2018 was the largest defensive improvement in baseball by more than two full runs and the largest among full-time outfielders by nearly 10 runs.

Harper has always been better coming in or going back on the ball. Side-to-side isn't his strength. In 2018, he was a negative in all directions. Coming in, going back, to his left, his right, whatever. Last season everything returned to normal. Good coming in and going back, not-so-good side-to-side. In the field, 2019 Harper looked a lot like 2013-17 Harper. 2018 stands out as the outlier.

"Everybody made such a stink about my defense last year," Harper told's Todd Zolecki last September. "This year, I took pride in it and really want to get better. My pitchers deserve that, and my team deserves that. I'll keep trying to get better every year."  

Teoscar Hernandez
TOR • CF • 37
2019 stats
View Profile

It's not often a player moves to a more demanding position and gets better defensively, but that's what happened with Blue Jays outfielder Teoscar Hernandez last year. He started the season in left field, earned a demotion to Triple-A in mid May -- Hernandez was hitting .189/.262/.299 the day he demoted -- then returned as a center fielder in early June.

"Pretty much every outfielder goes one way better than the other, so we had some discussions about that and some discussions about where to play guys and depth and things like that," Blue Jays first base and outfield coach Mark Budzinski told the Toronto Star's Laura Armstrong last June. "He's taken everything well, he's worked on his drop step going back on balls, he's gotten better and better. He's a great athlete and I think he also just needed to continue to gain confidence, which he has."

For Hernandez, the move to center field was a homecoming. He came up through the minors as a center fielder and only started playing the corners regularly at Double-A and Triple-A in 2016, as the Astros moved him around to improve his versatility. Houston traded Hernandez to the Blue Jays in 2017 and in the corners he remained up until last June.

Hernandez put up minus-17.1 runs defensively as a most-of-the-time player in 2018, making him one of the worst outfielders in the sport. Last year he improved to minus-5.4 runs with the shift to center field. That is still below-average, for sure, but it represents a huge improvement and a good step in the right direction. Only one outfielder improved their defense more from 2018 to 2019:

  1. Bryce Harper: +21.2 runs (minus-18.1 to plus 3.0)
  2. Teoscar Hernandez: +11.7 runs (minus-17.1 to minus-5.4)
  3. George Springer: +11.2 runs (minus-4.8 to plus-6.4)
  4. Hunter Renfroe: +10.5 runs (minus-5.4 to plus-5.1)
  5. Ronald Acuna Jr.: +9.3 runs (minus-7.8 to plus-1.5)

The move to center field put Hernandez back into his more natural and comfortable position, and his defense improved. His bat came around too. Hernandez hit .234/.310/.511 with 24 home runs in 91 games after being recalled. It's amazing what can happen when you put a player's mind at ease. The position change is a tangible reason to believe Hernandez's defensive improvement is real and not a small sample size fluke.

"I can use my speed more in center because I've got more space to cover," Hernandez told Armstrong. "And it gives me more chances to increase my skills and to keep developing what I feel that I have to improve in the outfield."