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Aledmys Diaz is Cooling Off

The best SS in the world in April looked very average in May. What is his floor? What is happening with him and what will he look like going forward?

St. Louis Cardinals v Milwaukee Brewers
Here's our guy making a nice follow-through on a single.
Photo by Mike McGinnis/Getty Images

The number one shortstop in baseball in terms of offense in April was Aledmys Diaz. His wRC+ was a crazy 219. In his first month in the majors, no less. Fantasy owners flocked to an elite hitter with the coveted SS eligibility. Manny Machado was second that month, with a wRC+ of 185. Remember Trevor Story's crazy start to the season? He was third at 147, a full 72 points of wRC+ behind Diaz, which is a whole Jimmy Rollins or two Alcides Escobars.

While most owners knew this ride would end some time (hello 0.413 BABIP), no one knew when it would happen and what he would look like once things settled down. Well, we have a better idea now what a "normal" Diaz looks like. Let's take a look at his May stats and see if it is time to sell high or hold on this fast-starting shortstop.

Table time!

April 75 0.423 0.453 0.732 0.413 0.31 19% 46.30% 4 5.30% 5.30% 41.80%
May 115 0.267 0.304 0.419 0.284 0.152 9.40% 48.90% 3 14.80% 5.20% 27.50%

Here you can see some of my favorite stats from April and then from May. These are arbitrary cut-offs and small samples, so keep that in mind. In just about every stat, you see big regression. He now looks like an average-hitting shortstop. We all knew there would be a drop off, but this is a big change. Sure, the BABIP went from very lucky to somewhat unlucky, but that doesn't necessarily explain it all. His HR/FB ratio returning to league average certainly played a role also. His ground ball rate is up and his hard hit rate went from 2015 Bryce Harper to 2015 Rajai Davis, which is not good.

Now, let's look at how pitchers have been pitching to him in both months.

This is his April plot:

Here's May:

You can see pitchers have moved to a little corner down and away.

Here you can see why they would do that:

His ISO in that lower right corner is pretty bad. His Slugging % heat map looks very similar. The book is out on him now.

Let's look at the pitches he has been seeing.

Zone % O-Swing % FB% SL% CT% CB% CH%
April 50.80% 26.70% 53.80% 25.40% 6.80% 5.70% 8.30%
May 47.60% 30.60% 58.10% 17.90% 3.80% 6.20% 12.40%

Pitchers are throwing him more pitches out of the zone and he is going after them. He isn't swinging and missing on them, but he is making lots of weak contact, which is just as bad.

The increase in fastball usage against him will become obvious with this table.

Season 0.19 5.02 1.98 6.04 2.88

You don't really need to know what wFB/C is to see that he does not do well against fastballs. These values are measures of his offensive production this year against different pitches, normalized to 100 pitches of that type. The higher the number, the better he does against those pitches. In general, pitchers are giving him less and less of the pitches he does well against and more of the ones he doesn't like.

His average fly ball and line drive exit velocity, according to Statcast, is 93.9 mph, which is very average (the leaders are near 100 mph). He is 115th on the home run and fly ball distance leaderboard. The reality is his power is just average.

The only minor league level where he spent significant time was AA last year, where he hit 0.264/0.324/0.421, with a 15-homer pace. That seems to better represent his abilities as a hitter and would be a good expectation moving forward. Now, 15 HR with 6-10 steals and that batting line is a top 10 SS, no question. It's not all that different from what Jhonny Peralta would give you, coincidentally (minus the steals).

The conclusion here is that he should be startable in all leagues the rest of the season, despite the recent slow down, but don't expect anything like April again. If you can get someone to buy him at his April price, by all means do it. Otherwise, enjoy a waiver wire solid shortstop for the rest of the year. It should be noted that Peralta will be back in the coming weeks, so Diaz may lose some playing time or shift over to second more often. That's another factor to consider here. The league's pitchers have adjusted to Diaz and he has still managed to be a good hitter for this position. That is a good sign, I think. Tschus!