# St. Louis Cardinals: How Aledmys Diaz Can Grow Offensively In 2017

#### By Zach Gifford

## Following an impressive rookie season, the St. Louis Cardinals will count on Aledmys Diaz to help set the tone at the top of the batting order this year. How can he adjust his swing to maximize his offensive output in 2017 and beyond?

After a power surge in 2016, the St. Louis Cardinals offense will have an on-base focus in 2017. Dexter Fowler and Matt Carpenter have both established themselves as .360+ OBP hitters, while the less-proven Stephen Piscotty and Aledmys Diaz check in around .350 or better. This Cardinals lineup, especially at the top of the order, should be better at manufacturing runs without the need for the long-ball.

Of course, for this lineup to perform up to its potential, each of the top four must repeat or improve upon their past performance. The biggest question mark among those four is Aledmys Diaz.

Diaz, almost literally, came out of nowhere. He was designated for assignment in July of 2015, before going on a tear to finish that season. You know the drill from there.

Had Diaz not fractured his thumb in August, he likely would have factored in the NL Rookie of the Year race. Now, the St. Louis Cardinals will count on him to repeat his offensive season while moving to the two- or three-hole in the order. Unfortunately, it is unlikely that he can replicate his success at the dish unless he improves his batted ball profile.

Earlier this week, I introduced a line of “expected stats” in an analysis of contact quality against Mike Leake. Today, I’ll apply those stats to the batted ball profile of Aledmys Diaz. From this, I will determine how he performed relative to expectations based on his contact quality.

For those who are unfamiliar with my xSTAT model, I binned every tracked batted ball in 2015 and 2016 by exit velocity and launch angle using data available via Baseball Savant. I then used that to calculate an expected BABIP (xBABIP), an expected batting average on contact (xBACON), and an expected home runs per HR possible batted ball (xHR/pHR).

This is best explained visually (plus I really like this graphic), so below is the exit velocity and launch angle matrix for BACON.

Red areas are where batted balls are most likely to go for hits, and blue areas are where batted balls are least likely to be hits. The blue area at medium exit velocities and fly ball launch angles is the batted ball donut hole. Essentially, these batted balls are generally lazy fly balls, while harder hit balls at those angles go for home runs and weaker hit balls at those angles fall in for bloop hits.

Assigning Diaz 306 tracked batted balls to this matrix, I calculated the following expected batted ball stats, and compared them with his actual batted ball stats.

Based on this analysis, Aledmys Diaz significantly overperformed what we should have expected based on his batted ball profile. Unless Diaz improves his contact quality in 2017, he’s a candidate to see significant regression. If that’s the case, the St. Louis Cardinals order no longer looks so good.

We can also look at these expected stats by just exit velocity or just launch angle. To do this, I grouped batted balls into five degree bins between -20 and 60 degrees. Additionally, I separately grouped batted balls into exit velocity bins of five MPH. Breaking it down this way, it’s clear that launch angle was Diaz biggest problem last season.

The first graph shows the percentage of all batted balls hit at each bin. The second graph displays the league average BABIP and BACON at each bin. Diaz was worse than average at generating batted balls between -5 and 25 degrees, where both BABIP and BACON peak.

Diaz made up ground on his batting average by legging out infield hits at an absurd rate of 15.8%. That rate was more than double the league average of 6.3% and the average rate among shortstops of 7.2%. It would be unreasonable to expect Diaz to repeat that aspect of his performance.

If Diaz IFH% was closer to the average among shortstops, he would have had 12 less hits. Without those hits, his BABIP would have been .281, his BACON would have been .317, and his batting average would have been .270. While his slash line of .270/.339/.480 would still have rated above average, it would have been noticeably worse than his .300/.369/.510 actual line.

Additionally, Diaz hit more home runs than his xHR/pHR indicates he should have, based on the exit velocity and launch angles of his batted balls. xHR/pHR tracks every batted ball between approximately 14 and 50 degrees and determines a probability based on league data that a batted ball at each exit velocity and launch angle bin will be a home run.

The matrix looks like this:

And the probability by launch angle looks like this:

The probability that a batted ball will be a home run peaks between 25 and 30 degrees. Comparing this to Diaz launch angle profile shows that he was fairly efficient at hitting balls in this peak, yet his xHR/pHR of 12.2% was below his actual HR/pHR of 17.9%.

Diaz lower xHR/pHR is likely due to a lower than average exit velocity on his fly balls: he checked in at 90.3 MPH, while the league average was 91.1 MPH. Had his HR/pHR had fallen in at the 12.2% expected rate, he would have only hit 12 homers last season. These lost hits also would have trickled down to lower his batting average, on-base percentage, and slugging percentage.

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This is not to take away from Diaz exceptional rookie campaign for the St. Louis Cardinals. Even if he regresses offensively, there’s still a good chance he is an above average hitter compared to both shortstops and the rest of the league.

Rather, this just shows that Diaz has plenty of room for improvement. If he can get generate more contact at launch angles between 5 and 15 degrees even while just seeing his exit velocity stay flat, he can consistently be a one of the best hitters at the shortstop position.

Ben Markham has suggested that Diaz put conscious effort into generating more lift with his swing to fuel more power. If Diaz can generate more fly balls between 25 and 35 degree launch angles, he can maintain or improve his power output.

One player who has made a similar adjustment: Manny Machado. Back in 2013, Machado had a ground ball rate of 47.1% and fly ball rate of 32.3%. Since then, he’s added 10% to his FB% by dropping 10% off his GB%. Diaz had a 45.5% GB% and 38.9% FB%, but only a 15.6% line drive rate, compared to Machado’s 20.6% rate.

I’m not saying Diaz will be as good as Machado if he makes a similar adjustment. However, the gap between them in batted ball quality isn’t that large. Diaz average exit velocity in 2016 was 90.2 MPH, while Machado’s was 91.2 MPH. Additionally, their average exit velocities by launch angle follow a strikingly similar distribution:

With the preface that I’m not a scout and bad at editing, I analyzed film of Machado’s swing and compared it to Diaz in 2016.

I froze each video at or just after the moment of contact, and overlaid the photos to better show the comparison. The angle of Diaz shoulders (on left) is noticeably flatter than Machado’s, whose shoulders form a more vertical line.

As the swing is just finishing, there are three important distinctions. First, Diaz front foot is completely planted, which indicates his weight has shifted forward and is fairly evenly distributed. Compare that with Machado, whose weight is still shifted toward his back leg so much that he’s back on his heel.

Additionally, notice that Machado’s torso has slightly more lean toward home plate than Diaz. Further, while Diaz bat is fairly flat at the end of the swing, Machado points the bat at a steeper vertical angle. Machado’s swing clearly takes a more vertically oriented path and consequently generates more lift on batted balls. When he hits the ball in the air, he does so with authority.

The consequence in batted ball quality is obvious. Machado hit his fly balls at an average exit velocity of 93.5 MPH, more than 2 MPH harder than his average batted ball. Diaz, on the other hand, hit fly balls at an average exit velocity of 90.3 MPH, no better than his overall average of 90.2 MPH.

Next, I compared Machado’s swing in 2013 (left) to his swing in 2016 (right). It appears he’s made an adjustment to lift the ball and inflict more damage. Could Aledmys Diaz do the same?

In 2013, Machado’s front foot was completely planted, his bat was flatter at the finish, and he had a little less lean toward the plate. By 2016, he clearly adjusted his swing to lift the ball and maximize his batted ball damage.

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Aledmys Diaz showed an exceptional ability to adjust on the fly in 2016. He has had an entire offseason to scout himself, his swing, and how he can improve next year. If he can make further adjustments to improve his batted ball profile and maximize his offensive output and consistency, Diaz could be the St. Louis Cardinals most dangerous hitter.