Earlier this week, we expanded Outs Above Average, the primary Statcast defensive metric, to include infielders. Most of the rankings made a lot of sense -- Javier Báez and Nolan Arenado rate very well, Vladimir Guerrero Jr. does not, and so on -- but there was a name at the bottom that stood out to us in a shocking way. Fernando Tatís Jr., without question one of the most exciting young talents in baseball, came in rated as 2019's third-weakest infield defender, at minus-13 OAA. (Báez was plus-19, for comparison.) That's actually worse than it sounds, because this is a counting stat, and he missed half the season.

It's stunning, because you've seen what Tatís is capable of doing, and no one questions his athleticism. Still, that poor number is going to stand out, and suddenly the rumors that San Diego might be interested in Francisco Lindor -- pushing Tatís to center or multiple positions -- make a little more sense. That being the case, it felt like it was worth our time to dig into it a little more to explain what's happening here. What you want to know with a number like this comes down to two things:

1. Wait, really? You've seen him play, yes? That can't be right ... can it? 

2. Does this mean he can't play shortstop, or is there hope here? 

Basically, we need to know if this new metric is accurately capturing Tatís' 2019, and if so, how that happened -- and what it might mean for his future at the position.

1) Is this rating for real?

When we saw this on our internal list weeks ago, his ranking stood out so glaringly that we immediately ran to watch a ton of video to figure out if something was up with the data or the model. But then we realized that we didn't necessarily even need video to figure out what was going on, because the story was told in the most traditional stats of all. As summed up briefly in our introduction article ...

While 26 shortstops played more innings than his 731 1/3, no one in baseball at any position had more throwing errors than his 14.

So that tells you something right there, that Tatís made more than his share of mistakes per inning, and that a lot of them came on throws. But even that doesn't necessarily tell the entire story, because not all misplays get marked as errors, like this Nick Markakis single.

"More throwing errors than anyone in baseball while playing half as often as full-time shortstops" should probably get the point across here well enough, but we can do better than that.

So here's what we did. With Outs Above Average, every play is given an estimated probability of becoming an out, based on factors like the distance the fielder must go, the time he has to get there, the distance he then is from the bag on force throws, the speed of the runner, and so on. A low probability (like 10%) is a difficult play. A high probability (like 90%) is considered an easy play. (This is all broken down in further detail here.)

Then, we found every misplay from Tatís with an estimated success rate of 50% or higher, which is to say, opportunities that turn into outs more than half the time across the Majors. We're ignoring whether it was scored a hit or an error, because it isn't really relevant here. It's just "was the play made, or not?"

For Tatís, there were 39 such plays, or one every 19 innings. We cherry-picked a few other notable shortstops to compare in order to put that number into context.

Misplays of opportunities with an estimated success rate of 50% or higher, 2019

Tatís: 39 misplays in 731 1/3 innings (one every 19 innings)
Brandon Crawford: 38 misplays in 1,233 innings (one every 32 innings)
Amed Rosario: 35 in 1,337 1/3 innings (one every 38 innings)
Marcus Semien: 34 misplays in 1,435 innings (one every 42 innings)
Xander Bogaerts: 31 misplays in 1,368 innings (one every 44 innings)
Javier Báez: 19 misplays in 1,116 2/3 innings (one every 59 innings)
Paul DeJong: 22 misplays in 1,372 innings (one every 62 innings)
Andrelton Simmons: 11 in 873 1/3 innings (one every 79 innings)

You get the idea here. The best shortstops are missing these kind of higher probability plays maybe once a week, if even. The middle of the road guys are doing it once every five games or so. Tatís was having it happen once every other game, and again, it's not just about errors, as this throw on a Nolan Arenado single shows.

So, is it real? Yeah. Despite our initial surprise, and all of the highlight-reel worthy plays he makes otherwise, the sheer number of mistakes makes the negative rating make sense. It's difficult to be a top-quality shortstop with this many miscues.

Now, as you are surely pointing out: Tatís turned all of 21 years old in January. It was a surprise that he even made the San Diego Opening Day roster last year, and his rookie season, while often exhilarating, was also interrupted by injuries to his hamstring and back. If what we saw was merely the first step of many to come, that would be perfectly understandable. He'd hardly be the first super-talented player to debut at a young age and then improve with health and experience.

So let's look at those 39 misplays and other associated errors, and try to get to how they happened -- and if they can be avoided.

2) Does this mean he can't be a shortstop?

We're thinking here about how Ryan Braun got to play third base for one year in 2007, then never ever again, because it was clear he simply couldn't do it. Is that what's going to happen to Tatís?

We can't say for sure what the future holds, though the Lindor rumors have to tell you a little something. But what we can do is try to figure out if the mistakes were telling you that he didn't have the range or skill to get to the ball, or if it's something else.

To that end, we watched each of the 39 plays. Only 11 of them were about an inability to collect the ball, and one was a bad route on a pop-up on a sunny day. That left 26 of them coming on throws, which again, should not be surprising -- as we said, he had 14 throwing errors.

It's not about arm strength, obviously. It just seems to be about rushing, sometimes poor footwork, but also in many cases just trying to make a throw on a play that has no business even being attempted.

For some examples, here's your run-of-the-mill off-target throw:

Here's a slick dive that turned into a spin and a wild throw:

Here's a throw on the run that pulled Eric Hosmer off the bag, turning an easy third out into a rally:

... and so on. Basically, it seems like he could do a lot more by doing a whole lot less, and we can just about guarantee that's not the first time that's been said about an electric young player's rookie season.

The takeaway here ought to be that despite all of the great plays you saw in 2019, he was an overall poor defender -- but that doesn't mean he will be. Tatís doesn't appear to have much difficulty getting to balls, which is something you're more likely to see in slower or older players and is a much bigger problem, because it's a lot harder to overcome. It's just that when he gets there, he's not always making the best decisions or the most accurate throws. The strength is there, and the talent is too. It's not hard to see the production following, with just a little more experience.