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How Aledmys Diaz can get more out of his high Exit Velocity in 2017

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Diaz hits the ball hard a lot, but could stand to improve on what angle he hits them at.

MLB: Cincinnati Reds at St. Louis Cardinals Jeff Curry-USA TODAY Sports

Aledmys Diaz, man. In 2016, he was the reason for fans of other teams to hate the Cardinals. Jhonny Peralta has a down year in 2015, and then gets injured early on in Spring Training. The ghost of Ruben Tejada was the best piece available, so the Cards pick him up, only for Tejada to injure himself as well. “No problem” says Aledmys Diaz, “I’ll just have the best first month of a career in baseball history”. Things cooled at times for Diaz, but he still finished with a strong rookie season:

To start off with, Diaz combines a slightly above-average walk rate with a very low strikeout rate. That gave him the fourth best non-contact wOBA on the team, behind Kolten Wong, Greg Garcia, and Matt Carpenter. He also hit for a well above-average rate of power, and enjoyed an above-average rate of hits on balls in play.

The power, in terms of home runs at least, looks for real. We’ve talked before about average Fly Ball and Line Drive Exit Velocity (avg FB/LD EV) before, tracked by MLB’s Statcast technology and hosted at BaseballSavant.com. While Statcast has only been in place for a couple of years, it turns out that a player’s performance in this stat in 2015 said more about a player’s home run production in 2016 than there actual production in 2015. Diaz’s home run per fly ball rate (HR/FB%) was 12.6%. His avg FB/LD EV was 92.7 MPH, which gives us an expected HR/FB% of 13.2%. Those are both right around average marks as the league average HR/FB% in 2016 was 12.8%.

The reason for the well above-average power was the two other extra base hit types. Diaz hit 28 doubles and 3 triples, compared to 17 homers. In-play extra base hits made up 40% of his ISO. That seems like a spot where Diaz’s ISO could regress. However, there is some room for growth in Diaz’s power profile. Let’s put it this way. Diaz’s overall Exit Velocity was 90.2 MPH, an above-average mark that ties him with nine other players for spots 150-158 out 487 hitters on Baseball Savant’s leaderboards. However, things look different when breaking down his velocity:

Of nine players with a 90.2 MPH Exit Velocity, he has the fourth lowest Exit Velocity on flies and line drives. That doesn’t sound that bad, but Wilmer Difo and Anthony Gose only made the list because of a very low cut-off for Statcast-tracked batted balls. Diaz’s avg FB/LD EV was only a tick above the 91.8 MPH simple average in the stat. “EV diff” is the difference between that and the avg GB EV (average ground ball Exit Velocity). The simple average difference between the two was about 5.5 MPH. Diaz doesn’t need to learn to hit the ball harder, he already does. If he can learn to distribute his Exit Velocity better though, he could sustain a higher HR/FB%, and possibly hit for even more power in 2017.

This would likely come to the detriment of his results on balls in play, but the trade-off is worth it. Here’s a chart I posted a couple of times before, but it’s relevant to this discussion:

Generally, a hitter should want his hardest hit balls to come between about 10 and 35 degrees, as that’s where hard hit balls are most valuable. From 25 to 35 degrees is where the difference in value between hard hit balls and weakly hit balls is the largest. Statcast categorizes batted balls under 10 degrees as grounders, 10 to 25 degrees as line drives, 25 to 50 degrees as fly balls, and above 50 as pop-ups.

With that in mind, let’s look at Diaz’s batted ball profile, using some neat graphics from Baseball Savant:

Here’s the bad news: this is not what a player with an above average BABIP looks like. On average, hitters put 14.7% of their batted balls over 35 degrees, where value starts to drop off considerably in the graph above. Diaz hit 18.3% of his batted balls over 35 degrees. That might not sound all that bad, but batted balls between 35 and 40 degrees average a BABIP of just .069. He doesn’t make up for it by avoiding low-angled grounders, as you can see by the large spike at -10 degrees. Batted balls under -10 degrees have an average BABIP of .122. Between -5 and -10 is .241 Overall, Diaz hits low angled grounders at about the average rate.

The graphic on the right shows Diaz’s average Exit Velocity at each angle. His swing seems to be geared around hitting the ball the hardest at 0 degrees, not exactly an angle where you can do a lot of damage. That’s where Diaz could use a change. As the graph above shows, even hard hit balls at 0 degrees aren’t all that valuable. If Diaz can make an adjustment that allows him to concentrate more of his hard hit batted balls in the air, and we could see a big boost in homers from Diaz.

Take Jedd Gyorko for instance. He commanded only a 88.1 MPH average Exit Velocity, 2 MPH lower than Diaz. Somehow, he managed to hit his flies and liners at an average of 93.3 MPH, a little more than a half a MPH better than Diaz. Jhonny Peralta had strikingly similar results. Stephen Piscotty also had a lower total average Exit Velocity but a higher flies and liner Exit Velocity than Diaz. Matt Carpenter hits the ball harder than Diaz overall, but had a 9 MPH difference between his flies and liners and his grounders, double the difference of Diaz.

A conscious effort to get the ball in the air more should fuel more power, but could come with more pop-ups. However, it could also come with less low-angled grounders, limiting the damage done to his BABIP abilities. Normally, I don’t recommend players change their swing. The majors isn’t the best place to re-learn how to hit. But this seems to be an adjustment being made across the majors, including the Cardinals’ clubhouse. Diaz hits the ball hard. The stats just verify everyone’s eye test. He could, however, stand to adjust where he hits those hard hit balls.