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What’s Going on with Aledmys Diaz?

Aledmy Diaz was a breakout star with the bat in 2016. So why was April 2017 such a bummer?

St Louis Cardinals v Milwaukee Brewers Photo by Dylan Buell/Getty Images

Probably the biggest positive surprise to come out of the otherwise disappointing 2016 season was the unexpected breakout of Aledmys Diaz. Okay, let’s be honest; we probably don’t need that probably. It was an incredibly frustrating year, and the sudden emergence of a shortstop with a 130 wRC+ bat was easily the biggest positive surprise.

Of course, the breakout wasn’t without some accompanying warts. Diaz’s defense was, at times, a liability. And maybe that at times is kind of like that probably up at the beginning of the column, as in we don’t really need the qualifier. Although, in fairness, Aledmys did play steadier defense later on in the season; it was just never anything more than steady, at best.

Overall, though, Aledmys Diaz in 2016 qualifies as both a huge surprise, and a long-term positive development for the club, one of the very few we saw. Most 2016 performances were either disappointing or pointed toward future disappointment; Jedd Gyorko and Diaz were probably the only positive surprises, at least on the position side of things.

Now the real bad news: Aledmys Diaz has not been very good at all so far in 2017. That 132 wRC+ of 2016 was always likely to come down a bit, but in a depressing piece of baseball symmetry, Diaz’s 2017 wRC+ is 66, or exactly half of his 2016 number. That’s...pretty bad.

So what’s the story, morning glory?

Well, first off, we can look at Diaz’s peripheral numbers and see an instant red flag: the walk rate. In 2016, Aledmys drew a walk in a very respectable 8.9% of his plate appearances. That was better than the league average mark of 8.2%, but what really made that number stand out was how it related to his strikeout rate. The average K rate across baseball in 2016 was 21.1%; Diaz whiffed in just 13% of his trips to the plate. That slightly above-average walk rate on its own looks pretty good, especially from a shortstop; combined with a strikeout rate less than two-thirds the league average you really have something exciting on your hands.

Now, for 2017. The strikeout rate for Diaz is just fine; in fact, it’s actually even better than in ‘16. So far this year the league average strikeout rate is 21.6%, which Aledmys is absolutely lapping with a miniscule (relatively speaking), K rate of 10.7%. So he’s striking out less than half as often as an average major league hitter this season. That’s good. He’s also walked in just 1.9% of his plate appearances in 2017. That’s...not as good. Okay, it’s just bad. Actually, it’s flat-out terrible, if we refuse to mince words.

There is some more encouraging news on the peripheral front, though. Diaz’s batting average on balls in play this season is an horrific .200. That has to come up. And will come up. And when it does, the low strikeout rate will make Aledmys a high batting average hitter again. Well, hopefully.

Here’s the really concerning thing about Diaz’s profile so far in 2017: he’s swinging at everything. Well, not literally everything, but way, way more pitches than he did last season.

In 2016, Aledmys swung at 45.2% of all pitches he saw. For reference, that’s somewhat aggressive, but not extremely. Matt Carpenter’s career swing% is 37.0%; Yadier Molina’s is 51.6%. So Diaz was somewhere between super patient and super aggressive.

In 2017, however, Diaz has swung at 55.5% of pitches thrown his way, which is an enormous jump. We’re talking close to a 25% jump in swing rate from last season to this year. Now, he has gone from a 66.7% z-swing rate (z-swing% being pitches inside the strike zone), to 72.3%, which isn’t really a problem. Swinging at more strikes is, generally, fine. Sure, there’s a point where you’re probably swinging at pitches you should take even within the zone, but so long as the pitch is a strike it’s hard to really fault a player for swinging at it.

There is, unfortunately, worse news on the swing front. O-swing%, as I’m sure you can guess, is the percentage of pitches outside the zone a hitter swings at. Obviously, a hitter is going to swing at some balls no matter how selective and disciplined he is, but the lower the number on O-swing%, generally speaking, the better.

Diaz’s O-swing% in 2016 was 26.3%, which is pretty good. It’s only a few percentage points higher than we see from ultra-patient hitters like Dexter Fowler and Matt Carpenter.

Diaz’s O-swing% in 2017: 40.1%.

You want to know why Aledmys Diaz doesn’t look like the same hitter in 2017 as he did in 2016? And you want that knowledge condensed into a single number? Well, the number is 40.1. Diaz is chasing balls out of the zone at an appalling rate so far this year.

The rest of Diaz’s plate discipline and contact numbers are right about where they were last season. His contact rate on balls is up from 65% to 66.2%, which is fairly negligible, but doesn’t exactly help when he’s swing at 50% more balls overall. His contact rate on strikes is identical to last year. He’s seeing roughly the same number of strikes and balls this year as last (there is less than a one percentage point difference in the number of pitches in the zone he’s seen this year versus 2016), and it making contact with pretty close to the same number of pitches in toto. It’s just that his ability to control the strike zone this year, and swing only at pitches he should be swinging at, has seemingly deserted him.

As far as the batted-ball profile goes, Diaz is making less hard contact (26.7% vs 31.5% last year), has hit fewer line drives (11.1% vs 15.6%), and is pulling the ball more (51.1% vs 46.3%). Interestingly, he’s hitting the ball in the air quite a bit more, having increased his flyball% from just under 39% to 45.6% in 2017, so perhaps he’s attempting to make the change so many other hitters in baseball appear to be going for the last couple seasons, deliberately shooting for pull-side contact in the air. We saw Jedd Gyorko make a similar move last season, and it seems to have paid dividends for him. Perhaps there’s an adjustment in approach going on with Aledmys as well, and we just haven’t seen the full benefits take root yet. I will note that Diaz’s five home runs, four doubles, and .188 ISO are really the only things buoying his offensive value the slightest bit so far this season, so if he’s selling out for power at least the power is occasionally showing up.

Overall, though, what we’ve seen from Diaz is weaker contact, lower exit velocities in general, and more contact being made on pitches he should be letting go by. I opined not long ago that it looks to me like Aledmys is severely off-balance in terms of his swing this year; even on pitches he takes he’s falling across the plate the majority of the time. This could all be just a simple pitch recognition/selection issue, but I tend to think what we’re seeing is more a mechanical issue that’s putting Diaz in a poor position to make those decisions. I don’t think he’s simply failing to identify good pitches at which to swing this year; I think the fact his swing is out of whack is keeping him from being able to identify those good pitches to go after. His head is moving, his feet are moving, his torso is moving. There’s no stability in Diaz’s swing so far this year, it seems, and I believe his lack of a stable base to work from is causing the issues we see.

I’ll leave you with a couple heatmaps from the always-excellent Brooks Baseball that should give some idea of what we’re dealing with here.

First, this is the percentage of pitches Diaz swung at in 2016:

which, yeah. That’s pretty great. We see a huge number of pitches down and away — 161 out of the zone down and away is the highest single number on the board — and Diaz mostly laid off them. When pitchers threw strikes, he attacked. When pitchers tries to come over the middle of the plate or challenge him inside, he attacked with a vengeance. He swung at the pitches you want him to, mostly.

Now, let’s move to 2017:

And that is....not as good. Diaz is swinging at way more pitches on the outside edge of the plate. He’s swinging at more pitches down below the zone. He’s swinging at way more pitches inside off the plate, where he’s only going to get jammed when he makes contact. Those balls way down and away out of the zone he’s still mostly laying off, but pretty much anything else even close he’s going after. This is what it looks like when a hitter isn’t controlling the zone at all.

So how concerned should we be? That’s a tough question, honestly. Diaz is obviously expanding his zone to a terrible degree, and that’s bad. The interesting thing is it doesn’t really seem, judging by any data we have readily available, that pitchers are approaching him all that differently this year. He’s seen slightly more cutters this season than last, but he hasn’t seen a huge jump in offspeed pitch percentage generally. Pitchers are throwing him roughly the same amount of strikes this year. If anything, they might actually be challenging him a bit more, which could be worrisome if we think that’s an indication opposing pitchers think Aledmys is less dangerous than he was before. But really, things aren’t that different in terms of what he’s seeing. It’s what Diaz is doing with what he’s seeing that is so different.

As I said earlier, I think this is a mechanical issue bleeding into the approach. I could be wrong, obviously, but I believe if Diaz can get his swing back in balance where it was last season, his pitch recognition should improve markedly. However, I have to admit to being a little concerned. A 2% walk rate, even over the course of one month, just isn’t a thing that should happen. Losing zone judgment to the point of swinging at 50% more balls really shouldn’t either. Players slump all the time, but to lose all discipline the way Diaz has this season is honestly pretty scary.

Hopefully, the issue will resolve itself relatively soon. And the increased flyball percentage is intriguing, in the sense that if Diaz can continue to trade in grounders for flies, he could be in for a further power breakout, considering the exit velocities he routinely produced last season. But before we can think about that, we really need to see Aledmys Diaz find his strike zone again.

And, you know, just let a pitch go by every now and then.