By this point in time you’ve probably read a little bit about Yankees’ shortstop Didi Gregorius.
Perhaps its an article singing his praises, maybe even one dubbing him as a dark horse MVP candidate in the AL. He is, after all, hitting a ridiculous .354/.452/.793 through his first 104 plate appearances this year. His ability to get on base, a huge reason why I considered him to be rather overrated before the start of this year, has seemingly drastically improved. Though a player’s walk rate usually stabilizes at 120 PA, Didi has already walked 17 times in 2018 compared to a horrendous 44 total times in 1167 PA the past 2 seasons, leading to a paltry .311 OBP from 2016-2017.
Perhaps it’s an article expressing skepticism of Gregorius’ success. In an era beginning to revolve around exit velocity, Gregorius hits the ball extremely softly. Out of 281 players to put the ball into play 200 times in 2017, Gregorius’ 84.4 MPH average exit velocity ranked 250th in baseball. This led to an expected wOBA (xwOBA) of just .293 in 2017, or 271st out of 330 hitters with 200 AB, grouping him close to some of the league’s worst hitter in this specific category. The low xwOBA was partly due to the low walk rate, but heavily aided by Gregorius’ inability to hit the ball with any emphasis whatsoever. Gregorius’ actual wOBA was .335, putting him in the upper 40% in baseball, which leaves quite a discrepancy. This .042 gap between Gregorius’ xwOBA and wOBA was the 14th biggest in all of baseball and is similar to that of some of the league’s fastest players like Mallex Smith, Dee Gordon, Delino DeShields, Kevin Kiermaier, Jose Altuve, Charlie Blackmon, etc. The gap in those 2 statistics is a lot easier to swallow when you consider these players frequently use their speed to beat out hits that should be outs or take more bases on an XBH than an average player would.
Didi is at it again in 2018. Of 180 players to put the ball into play 50 times this season, Didi’s 87.2 mph average exit velocity ranks 136th, creating a 0.058 gap between his xwOBA and actual wOBA, the 4th highest “overperformance” in baseball. So what gives? How is this guy so consistently overperforming despite hitting the ball with zero oomph?
One theory is Yankee Stadium. If you don’t already know, the new Yankee Stadium is notorious for having an extremely close wall out in right field. Here are all the parks in Major League Baseball overlapped:
Note the right field wall in Yankee Stadium, which shouldn’t be hard to find as it is wildly closer to home plate than ~28 other stadiums for a stretch of upwards of 100 feet. For a pull-happy, left-handed hitter, you could see why that would be rather beneficial, and sure enough, Gregorius fits this mold perfectly. Here’s his spray chart from 2017:
Ballpark diagram credit: Lou Sporito at THIRTY81 Project
To a degree, I buy into this theory completely. Of Gregorius’ 12 HR at Yankee Stadium in 2017, just 2 went farther than 400 feet. So far this season, all of his home runs have come at Yankee Stadium and a third of them failed to go 350 feet and still somehow cleared the fence. I don’t have the data for every last hit trajectory for Gregorius or the park data to be able to overlap the dimensions and tell you which of his hits were because of the park itself and which ones were legitimate. What I can tell you is that shots like this only leave the park in Yankee Stadium:
I could probably mine that data and sort through it all and give you some sort of hard evidence, but that isn’t the point of this article, nor would it necessarily lead to any drastic conclusions at the end of many hours of work. Do I think Gregorius would put up the same numbers in a different stadium? I absolutely do not, and hopefully someday baseball statisticians 10 times smarter than I can find a good way to implement park dimensions into OPS+ or something similar. But Gregorius’ numbers aren’t fueled by Yankee Stadium; he still holds an expected wOBA close to .500 this season, and that doesn’t happen by accident, with the help of your park, or some combination of both.
It’s because Didi Gregorius is the king of launch angle.
Of all 180 players with 50 balls in play this season, Didi’s name is shoved right there near the top at #6 with an average launch angle of 21.6 degrees. That’s great, and obviously explains not only the good expected wOBA, but the on-the-field results as well. But if he’s #6 in average launch angle, how is he the king? Wouldn’t hitters 1-5 in that category have better claim to the throne? Well when it comes to launch angle, the average isn’t always what is most important. Ask a darts player; you can’t live on accuracy alone. You need precision as well.
Let’s take Didi and compare his launch angles to 4 of the other 8 hitters who, at the time of writing this (4/26)* are currently launching the ball on average 20 degrees or better: Mike Trout, Mookie Betts, Joey Gallo, and Mitch Haniger. Hopefully, if you’re reading this, you already know Mike Trout is the best player on planet Earth and it isn’t close. Mookie Betts is one of the best players in the league – dare I say the second best player in baseball – and the other two are extremely good players as well, albeit in much different ways. Let’s take a look at their launch angle charts:
Note that the scales in which these fans are presented are not the same, a small but important detail. Trout and Gallo’s only go up to 7 balls in play and Mookie and Haniger’s top out at 8. The first thing you should notice is that these launch angle charts for all 4 hitters who all average the same launch angle are wildly different, Haniger’s and Gallo’s especially. Which, hopefully, illustrates my point. There are, literally, infinite different ways a hitter could hit balls into play and still manage to have his average launch angle technically round out to 20 degrees or better. That doesn’t mean everyone with the same launch angle is hitting the ball equally well. Let’s take Gallo, for example. He has a nice solid red area in his spray chart (hits) between 10 and 30 degrees. Beautiful. But also, he has something north of 30 balls in play that were below 0 degrees or above 40 degrees that, not surprisingly, didn’t go for hits.
Which bring us to Didi’s launch angle chart:
Again, note the scale of the chart. Where as our 4 sluggers prior ranged from 7-8 ball in play maximum at any given angle, Gregorius’ chart scales up to 12 balls in play at around 25 degrees. Gregorius is living in the 20-30 degree angle zone, and despite his low exit velocities, he’s getting results. The density of his hits between (roughly) 15-25 degrees is absurd. Maybe it’s coincidence, but maybe Gregorius is onto something.
The correlation (in this insanely small sample of a much bigger population) between SLG% and the amount of balls hit between 20-30 degrees is actually quite good (and I may even look into it further), especially when you conder Joey Gallo gets shifted on more than anyone in baseball and figures to be a bit of an outlier. Of these players, no one hits in that launch angle zone more than Gregorius. Didi hit 71 balls between 20-30 degrees in 2017 as well. His ISO in these 71 instances was 0.704.
It will probably good to revisit this in a month when stats and batted ball profiles have calmed a bit, as it’s still very early and batted profiles are still somewhat small samples in the grand scheme of a season. It is also plausible that the Yankee Stadium theory will prove true, as the Yankee will play 15 of their next 24 games away from Didi’s playground. But maybe, just maybe, Gregorius has single handedly optimized the launch angle for hitters who lack elite exit velocity. As long as players like Mike Trout and Aaron Judge are in the Major Leagues, there will always be better and more feared hitters in baseball than Didi Gregorius. However when it comes to launch angle, Didi Gregorius may be wearing the crown.
*At the time of publish, Haniger’s launch angle had dropped below 20 degrees, but not by much. The example still applies.
Spray charts and launch angle charts per Baseball Savant
Photo credit: Getty Images