MLB: How MLB Pitchers Helped Didi Gregorius Break Out

Pitchers may have spurred Yankees shortstop Didi Gregorius’ break out

Acquired in a three team trade back in 2015, the Yankees acquired the light-hitting Gregorius in the hope that they had found their long term replacement to future Hall-of-Famer Derek Jeter. To that point in his career, Gregorius had compiled just  a .243/.313/.366 batting line over parts of three seasons in the Majors, with just 13 home runs despite playing in the hitter friendly parks of Cincinnati and Arizona. Indeed, if we look at the first 3 and and a half years of Gregorius’ career (adding in Gregorius’ first season in NY), the Curacao native ranked 20th among qualified shortstops in WAR and had compiled just an 86 wRC+. 

From 2016-2017 Gregorius ranked 9th in WAR among qualified shortstops. 

In 2017, he ranked 6th.

That’s a dramatic shift and while there has been legitimate  defensive improvement from Gregorius, it has also come with a big jump in power and as a result his overall offensive output. No longer a slappy, glove first shortstop, Gregorius’ 45 home runs over the last 2 seasons ranks 3rd among all shortstops. 

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Now yes, Yankee stadium is one of the most hitter friendly parks in baseball and yes, players like Gregorius have been the biggest beneficiaries of the juiced ball and the fly-ball revolution over the last two seasons. All of these things are true (and in Gregorius’ case, have been documented) but there is something else to add to this story.

Pitchers have actually helped to make Gregorius better over the last two seasons. 

To demonstrate this, let’s use a series of tables and graphs. The first thing I want to present is Gregorius’ pitch values over the last two seasons. Pitch Values are a stat collected at Fangraphs which measures a players success against a particular pitch type. A score of zero is perfectly average, whereas a positive score is above average and negative score below average. 

Pitch Type 2016 2017
FB -0.90 -0.25
CB 0.70 1.81
SL 3.30 2.37
CH 2.48 3.10
As you can see, Gregorius has excelled at hitting off-speed pitches over the last two seasons, while grading out as a below average hitter against fastballs (sinkers not included here). Indeed, much of Gregorius production came against off-speed pitches over the last two seasons. However, while Gregorius was out there mashing breaking balls and change ups, MLB pitchers continued to increase the rate at which they threw these pitches:
Credit: Fangraphs.com

The graph above shows an 80 game (appx. half-season) rolling average of both Gregorius’ wRC+ and percentage of fastballs seen. There is a pattern there and it seems fairly clear, fastballs go down, production goes up and the opposite is true as well. On one level this seems intuitive – if a hitter starts to show some power you pitch him tougher and that usually means more breaking balls. However, much to Gregorius’ delight, increasing the rate of breaking balls thrown is actually pitching him easier. By throwing Gregorius more breaking balls, pitchers have actually helped Gregorius break out as a hitter. Along with the aid of Yankee stadium and some juiced baseballs, MLB pitchers have helped Gregorius jump from below average regular to a top 10 shortstop in baseball.

There is one final note that needs addressing and if you look at the massive upswing in fastball percentage (red line) to the right of the chart above, you can see a clear adjustment from the league. Let me show you why:

Credit: Brooks Baseball

That’s a lot of blue on that map and for a hitter, blue is bad. Baseball has recognized Didi’s struggles against fastballs and have adjusted accordingly. It took them a while to catch up however and for that, I’m sure Didi Gregorius says thank you. By throwing Gregorius more breaking balls, MLB pitchers have helped turn Didi Gregorius into a top 10 short stop in baseball.

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