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What to make of Aledmys Diaz on defense and fielding metrics

Can Diaz hack it at shortstop?

Mark J. Rebilas-USA TODAY Sports

Aledmys Diaz is on a ridiculous historical run that nobody has ever seen before. Seriously. Think of that great run by Albert Pujols in April 2001. Diaz has been better. What about when Bo Hart came up and had so many hits in his first month. Diaz has been better. Remember when Jeff Francouer went crazy and got himself on the cover of Sports Illustrated. Diaz beats him, too. Yasiel Puig in 2013, Devon Travis last year, and Trevor Story this season all pale in comparison to what Diaz has done in his first 19 games.

I know. I did the research over at FanGraphs looking for players with a similar OPS over their first 19 games.

I started with the past decade (2007-2016), looking at all players' who'd recorded at least 50 PA (Diaz has 66) over their first 19 games, all within the same season. Nothing. Then I went back another decade. Then another. Then another. I ended up going all the way back to 1913, when the Play Index begins. Not a single player had produced a mark within even 50 points of Diaz. (Note: When I ran the numbers yesterday for 18 games, I found just one player with an OPS to begin their career that was better than Diaz: Willie McCovey in 1959, who hit .418/.473/.821 to begin his career in July and August and bested Diaz's OPS after 18 games by .009.) It's pretty safe to say nobody has had an April quite like the one Diaz is having now.

That is amazing on offense and has changed the perception of whether Diaz's bat would play in the majors. It will. The projections already believe. On defense, we cannot be quite as confident. In the field we've seen the misplays and the errors. On the season, he has five errors, four of them due to inaccurate throws. Unfortunately, errors are not always a good representation of a player's defense as they do not take into account range, difficult plays made, and relatively easy plays not made due to not getting to the ball.

There are defensive metrics that account for these things as well as errors. The two most popular and most reliable are Defensive Runs Saved (DRS) and Ultimate Zone Rating (UZR). Right now Diaz is one run above average per DRS, which separates their stat by components for infielders which are double plays, good/bad plays, and runs saved. )For a better explanation, click here). Diaz's plus one is due to being a run above average on double plays.

UZR also has components for infielders: double plays, range, and errors. By UZR, DIaz is average on double plays, plus 1.5 for range, and negative 2.6 for errors for a total of negative 1.1. We have one rating that says plus one and one that says minus one. So what does that tell us?


Don't use defensive metrics with such a small sample size. My apologies if you felt the article was misleading in any way, but we should absolutely, positively not use these defensive metrics to inform any opinion we might have about the defense of Aledmys Diaz. Diaz's first 50 plate appearances tells us way more about his ability as a hitter than his first 100 innings as a shortstop. If you believe the defensive statistics tell us something, then you should also believe that Diaz will continue to hit well over .400 for the season.

Before we can have an accurate representation of a player's real talent level on defense, we need three years of data. Anything less and we are dealing with a lot of guesswork that does more to mislead than inform. At the and of the year, we might know a little, but we should not be too much more confident in them than we are right now. I looked at the defensive numbers so you don't have to. So what are we to do?

We can watch the games, but unless you are there in person focusing on Diaz before the pitch and then taking notes so that views don't become clouded over time, but that is not realistic. We can rely on scouting reports from people who do that, but that might not be realistic with Diaz either. What makes things doubly difficult for Diaz is that it is possible his play has changed over time due to his layoff and shoulder injury.

Take this information from a chat over at Baseball America:

His arm appears to be light for everyday duty on the left side of the infield over the long haul, according to our reports.

It's hard to say when those reports were collected, but his arm strength does not appear to be a problem. Accuracy perhaps, but his arm has plenty of strength. Over at Minor League Ball, John Sickels said, "Defense meets steady definition." Our prospect report said:

In the field, Diaz has good hands and an average arm, as well as decent range. Overall, he's a little short of what you want from a starting shortstop in the big leagues, if I'm being honest.

Back when Diaz signed, Joe Kehoskie had this to say,

By current ML shortstop standards, Diaz probably has the arm to stay at short, but his glove and range were lacking in Cuba. I didn't see enough of Diaz to get a sense of his decision-making.

At Fangraphs, Dan Farnsworth said:

He has enough fielding ability with good range and an average arm not to need a lot of thump, but he still can hit for close to average power. His arm plays up with his release and ability to throw from every angle, keeping him viable at shortstop or any other infield position. At worst he fits a utility profile perfectly, but I can still see him working into a starting role with above-average production if his hit tool fully translates.

And when Keith Law saw Diaz in the Arizona Fall League, he said,

when I saw him on defense I didn't think he'd be an above-average defender (although bear in mind a lot of players are gassed by then and don't look as good on defense as they might in June)

That caveat that Law makes is key. many have seen Diaz, but few have seen him enough over an extended amount of time when he is fully healthy to make a real determination. The Cardinals staff has had the opportunity to watch him over the last year, and in the coming months will get an extended look at Diaz to see if he can stick as a shortstop. The Cardinals are likely to make a determination on Diaz's skills at shortstop before the defensive metrics will. With all that in mind, it is likely best to take the advice of Joe Schwarz, and enjoy the ride.