What’s Up With Nolan Arenado’s Defense?

Heading into 2021, the question that loomed over Nolan Arenado concerned his bat. Could he remain productive outside of Coors Field? Roughly 40% into the season, the answer seems to be yes. Although his on-base and slugging percentage are down, handy wRC+ tells us that Arenado’s offensive output relative to the environment he’s in has remained consistent. On this front, he has been the star the Cardinals had hoped for.

On the other hand, I’m willing to bet good money that nobody was worried about Arenado’s glove. Altitude doesn’t affect one’s footwork or agility. We expected him to continue his life as one of the league’s best third basemen. And all things considered, he still is one of the league’s best third basemen. What follows isn’t the sound of panic, but rather a fact to keep in mind. Consider Arenado’s defensive numbers this season:

They’re… okay. Huh. That being average elicits this sort of reaction is a paean to Areando’s talent. When the three big defensive metrics all agree that his defense has taken a step back, though, you have to wonder – what’s going on? He’s no pumpkin at the hot corner, but he’s also not the superstar we’ve become accustomed to. Prorate his 2021 DRS to his 2019 workload in terms of innings fielded, and you’d wind up with 7 DRS after rounding up. That would represent the lowest mark of his career. Defensive metrics are imperfect and noisy, sure, but confronted with these changes, there’s probably some signal worth analyzing.

For this article, I’ll be focusing on Baseball Savant’s Outs Above Average. Our in-house metric is UZR, but it unfortunately doesn’t account for infield shifts, which will become relevant later on.

So, what does OAA say about Arenado’s glove-work this season? His total can be broken down in terms of the direction he traversed during a play – in, lateral towards third base, lateral towards first base, or back – which might give us a better sense of where he is falling behind compared to previous seasons:

A good chunk of these numbers aren’t out of line with Arenado’s career tendencies. He mainly earns his keep through diving stops followed by strong, accurate throws to first; as if to reassure us, he’s already amassed +3 OAA on plays to his left. Plays where he moves in or back constitute a small portion of his value. It appears as if Arenado has been merely mortal this season, worse overall but not lagging in any particular direction.

What does stand out, however, is the -4 OAA he’s accrued on plays towards third base. That’s on par with his 2017 season, but the major caveat here is the number of attempts: 117 back then, as opposed to 43 this season. This is one area where Arenado has been undeniably worse. But there’s another area that’s even clearer. Baseball Savant allows us to look at a fielder’s OAA by batter handedness. Here’s Arenado’s OAA per season since 2016, split between left- and right-handed batters:

As a third baseman, Arenado records most of his outs off batted balls from righties. But we can’t just ignore lefties, because he’s at a whopping -4 OAA against them when his full-season low is three higher. It’s not that lefties themselves are a hassle, though. It’s that facing a lefty forces him to position himself in a way he’s perhaps not comfortable with. What do teams love to do when a lefty is at the plate? They apply the shift, of course. Dissecting Arenado’s fielding versus lefties, -3 of his -4 OAA are from plays he made in shortstop territory, where third basemen are often placed to cover the hole a shift produces.

Getting even more specific, all -3 OAA are from plays when Arenado assumed the role of shortstop “straight up” – that is, he was closer to second base than he was to third, in the sense of a traditional shortstop:

What’s intriguing, though, is that Arenado isn’t spending more time at short. The Cardinals this season have shifted almost as often (418 times) as the Rockies have (406 times) against lefties, representing two of the lowest rates in the league. Plus, both teams were conservative even before the infamous trade. And when Arenado handled shortstop straight up last season, he at least broke even with a 0 OAA and a 52% success rate on plays with an estimated success rate of 51%. The burden on his shoulders is the same as before, yet 2021 is the odd year out.

I suppose it’s time to look at a couple plays Arenado has made as a traditional shortstop. His shakiness in that role has ranged from understandable to “Nolan, is that really you?” To start, here’s an example of the latter:

A slow roller with not much distance to cover, not to mention Josh Bell as the runner – yeah, that cost Arenado a lot in the eyes of Outs Above Average. There’s not much I can add onto this. Once in a while, even the best fall victim to lapses. Funnily enough, that isn’t the first time Arenado committed an error against a Josh Bell grounder this season:

Also not a good look! Shown these two clips, someone oblivious to the existence of Nolan Arenado would assume he’s a terrible fielder. I don’t have access to data on individual plays, but after fumbling around with the sliders on Baseball Savant, it seems like they both had an estimated success rate of at least 90%. With the way OAA is calculated, that means the two boners alone cost Arenado -1.80 or more on his seasonal total. It’s surprising, but at least provides us an explanation.

That doesn’t mean silly gaffs are solely to blame for Arenado’s deflated numbers, however. Outs Above Average penalizes fielders less for failing to convert difficult plays by design, but over time, they do add up. Fully embracing the ridiculousness, here’s yet another play featuring Josh Bell. I’m not totally ruling out Nationals’ devil magic as a contributing factor:

Even though Arenado is situated at shortstop, the heroic dive towards his left is reminiscent of one he’d make near third. It’s the sort of impressive play he’s executed before. But while the speed and alertness is present, Arenado’s throw sinks before it can reach the glove of Paul Goldschmidt. There’s little reason to blame him; a lesser third baseman might not have snared the ball in the first place. In analyzing his defense, though, there’s a inclination to wonder whether this is indicative of a larger issue. Is Arenado having trouble throwing to first? Maybe, but there are examples of smooth throws that just weren’t in time:

Is there anything else we can take away from the four GIFs? Honestly, not much. There are a bunch of other videos I viewed in preparation for this article, but none of them hinted at a fundamental issue within Arenado’s glove-work. Unlike Fernando Tatis Jr., whose errant throws accounted for much of his poor defensive ratings in 2019, we can only shrug at this situation. Arenado has made some glaring mistakes, and he’s also been less efficient at converting batted balls into outs.

He’s a bit worse in each category, which does or doesn’t bode well for his future depending on one’s perspective. That there’s no crucial flaw could be a sign that Arenado is fine. But based on his downturn, there’s also a worthy argument that this is an inflection point. According to research from the Sports Info Solutions blog, defensive performance “takes an even sharper decline following their age 30 season,” and well, Arenado is right on the cusp of that moment. It’s the question of Schrödinger’s Baseball Player all over again – in this case, when does a (relatively) struggling fielder cease to exist as a superposition of states?

One final note. There’s seemingly a dearth of jaw-dropping Arenado gems this season. He’s had a few opportunities. But as in this GIF, they haven’t translated into outs:

Considering (a) how much distance he needed to cover and (b) Yelich’s elite sprint speed, Arenado would have been awarded tons of credit had he succeeded. But alas, he was a few paces too late. Maybe a previous version of Arenado pulls this off. Maybe his inability so far to execute the toughest of plays is representative of a lesser defensive ceiling. Or maybe, it’s nothing at all, since his success rate so far is calculated from a small sample.

The bottom line is that, unfortunately, Nolan Arenado’s uncharacteristic defensive ratings are largely an enigma. Metrics like DRS, UZR, and OAA are still imperfect, and there’s a lot we don’t know with respect to his condition and overall health. He’s at least been healthy enough for it to not appear in headlines, but who knows, he might have stubbed his toe in the morning of that game against the Nationals.

In sum, I’m not too worried about Arenado. Select 10 plays from his career at random, and there’s a much greater chance you’ll end up with a bunch of successful, even phenomenal ones. It’s not like he’s gone from having a positive defensive number to an overwhelmingly negative one, à la Bryce Harper in 2018. His work in shortstop territory has been sloppy at times, but Arenado has always been competent, not great, there. Only time can tell whether this is a turning point or a blip.