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Aledmys Diaz: Extraordinary fastball hitter

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and a lot of other things about him

Gary A. Vasquez-USA TODAY Sports

Aledmys Diaz's MLB career has had a fascinating beginning to it. As he continues to hit well, Cardinal's nation and the rest of the baseball world continues to try to assess how good he is. Surely he's not as good as his current 189 wRC+, but what can we expect once the dust settles? In April, I wrote about how Diaz's start, while unsustainable, had some very encouraging signs, including above average plate discipline numbers, elite Exit Velocity numbers and strong average fly ball distance. I mentioned that the batted ball quality would likely regress, but was more reliable than simply having good luck in terms of balls in play for a month, like say Pete Kozma is September of 2012.

Those batted ball numbers have cooled off but are still comfortably above average; Out of 121 players with more than 80 tracked balls in play, Baseball Savant has him at 31st in average Exit Velocity, or just outside the top quarter of MLB hitters. Diaz is 99th out of 253 in average fly ball distance, or about the top 40%. He's also 17th out of 189 qualified hitters at Hard Hit%. These numbers (and all the numbers that follow) do not include his double and homer from last night.

Last week I wrote on how each Cardinals hitter's projections had changed, with Diaz leading the team with 13 points of wRC+ gained since the beginning of the year. Now it stands at 15, with a Zips and Steamer averaged projection right at a 100 wRC+. Trevor Story has only gained seven points thus far, so in all likelihood Diaz's stock has risen more than any other Major League player this year.

We don't know all that much for sure about Diaz, but there is a lot we can look at over his first 116 PA. At very least, we're getting an idea of what he's been like so far, and that gives us something to watch for going forward. One interesting thing, and maybe not so important over such a short sample, is that he does have a reverse split:

Again, over a little more than a hundred PA this isn't very meaningful, but at the very least we see that he's not just beating up on opposite-handed pitching. He walks twice as much against RHP, and is displaying much better contact quality, at least in terms of results.

One thing I was interested in, was how he has performed against specific pitches, so I headed over to Brooks Baseball:

Easily the neatest thing about this chart: So far, he has missed just 1.54% of Four-seam fastballs that he's swung at. Even more amazing: In April, he saw 106 four-seamers, swung at 44, and missed....zero! Major League pitching as a whole failed to sneak even one four-seam fastball by Diaz in the first month of his career, and that, to me makes a huge statement about his bat speed. He is swinging and missing a lot at change-ups and curve balls, with above average contact abilities against 2-seamers, cutters, and sliders.

Next, let's check out his Zone profile. Here, we'll stay on the topic of pitches faced, as his Zone profile probably doesn't say all that much when looking at quality of contact of 100+ plate appearances:

This is a pretty polarizing chart. Diaz is great at making contact at everything besides the bottom third of the strike zone and below. Against 84 pitches in the top two thirds of the zone, he has swung at missed at just three pitches! In 39 pitches in the bottom third, he's swung and missed at 7 pitches, working out to an 82% contact rate, short of the league average contact rate in the zone at 85.8%. So he's below average but it doesn't seem like a major problem. It's below the zone where he's having a lot of problems though, with 22 whiffs on 40 pitches, or just a 45% contact rate compared to 61.6% league average contact rate out of the zone.

Contact out of the zone on average isn't going to result in as good of contact as in zone, so that's a problem but he's not losing as much on those swings and misses as he would be if those pitches were in the zone. He's seen 135 pitches below the zone this year, good for a 29.6% Swing rate, just above the league average O-swing% of 27.6%. Brooks doesn't have an option for a league average heat map (that I can see anyway), but I'd bet that the swing% for pitches below the zone is higher than other out of the zone pitches, as that's where most pitchers are trying to get their swings and misses on stuff in the dirt. So Diaz seems very average in how often he swings at pitches below the zone.

Let's filter for hard pitches: fastballs, sinkers, and cutters:

Just eight swings and misses against the hard stuff all year. Like the unfiltered chart above, the swings and misses happen more often against pitches low in the zone. It's not quite as lopsided as the first one.

And here's against off-speed stuff:

When pitchers keep their change-up down (which is generally what pitcher always must do with a change-up), they have been able to get it by him pretty easily. In the bottom third of the zone, including off the plate and below the zone, he's missed 11 times on 18 pitches. It's only 18 pitches, but it's certainly something to watch going forward. Against pitches Brooks Baseball deemed curves and slow curves, Diaz has swung and missed at 8 of 19 pitches in the same area.

It sure seems like what we're seeing here is a hitter who is incredible at catching up to high velocity, but is having a tougher time with the slower stuff, and perhaps is having trouble hitting lower stuff as well, even if it's not off-speed. He's not having much trouble at all on the slower stuff when he makes contact though, averaging 92 mph Exit Velocity (EV) against the hard stuff but still 91.5 mph against slow stuff, with breaking stuff at 90.8. He's much more likely to put the ball in the air with the hard stuff though, with just a 41.7% GB rate against hard stuff, 51.9% against breaking stuff, and 62.5% against change-ups.

It sure seems like, going forward, a better way for opposing pitchers to approach Diaz would be to lower their fastball usage against Diaz, in favor of off-speed stuff. Generally, new hitters to the league get a lot of fastballs in the zone, and that's what they've been doing with Diaz as well. Diaz has passed that test with flying colors, and in the game of adjustments that is baseball, I'd expect him to get less of that going forward.

We've spent a lot of time on plate discipline and contact, as those numbers are more reliable at this point. But let's look at his Spray Chart:

One thing that jumps out to me is the amount of pulled grounders, though that's a common theme for many hitters. Diaz looks shift-able, but RHH aren't as easy to shift against as a first baseman will have much less range than a third baseman or shortstop who is left on one side of the infield when shifting against a lefty. Diaz has pulled all his home runs down the left field line, but he's hit deep fly balls (and line drives) all over the park, so I wouldn't say he only has pull power.

Maybe you can say this is only 116 PA, so what's the point. But Diaz has been a most unexpected offensive force over those plate appearances, and with so little track record for the nearly 26 year old Cuban, we could use something to go on. If for nothing else, this serves as reference point as time goes on and samples get larger. Diaz has been great at hitting fastballs, but is having problems both down in the zone and below it, particularly against off-speed stuff and slow curves, pitches that generally need to be in those areas to be effective. He's hitting everything hard when he hits it though.

It'll be interesting to see how Diaz continues to evolve as a hitter, and how pitchers adjust to him. He's also got a strong arm and enough range to play shortstop, along with the athleticism to make a lot of great highlight-worthy plays. As long as he slows down on booting more than his fair share of grounders, the Cardinals have their shortstop for the next several years.