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Jake Arrieta Is Not Your Normal Ace

Chicago Cubs pitcher Jake Arrieta capped off his impressive Cy Young case with the first no-hitter of his career late last month. Arrieta’s 2015 résumé lists a 1.99 ERA, 19 wins and the third-most wins above replacement (WAR) in the league.1 This incredible year builds on a 2014 season in which he was one of the top 10 pitchers in baseball. So it’s no surprise that this year, Arrieta has confirmed he’s an ace. But how he became one isn’t the usual story of a phenom flying through the minors and into hitters’ nightmares. Instead, it’s the story of a guy who kept changing the way he threw a baseball until everything started to click into place.

Two years ago, Arrieta was a near-replacement-level player, worth a win or so as a member of the Baltimore Orioles and Cubs. His career to that point had been lackluster. As a fifth-round draft pick, Arrieta had already exceeded expectations merely by making it to the majors, but his performance there hadn’t been especially impressive: Arrieta recorded a grand total of 3.1 WAR in 78 games spread over four years, never putting up an ERA better than 4.66.

While Arrieta’s surface stats were static and unimpressive, his mechanics were busy evolving. Where a pitcher releases the ball is one of his most important characteristics: High release points establish more downward plane on the ball, causing a pitch to sink as it enters the zone; release points far to the left or right create more horizontal motion through the zone.

Most of the time, the horizontal and vertical coordinates of a pitcher’s release point are fairly constant, determined largely by mechanics learned long before he made the majors. In Arrieta’s case, however, his release point changed the more time he spent in the bigs. Every year, Arrieta’s release point increased in height and moved further toward the third-base side of the pitching rubber. The total change is extreme: Arrieta moved his release horizontally across the rubber by nearly a foot and upward by nearly six inches.

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Since Arrieta didn’t get any taller or wider during that time, the variation in his release point means that his pitching mechanics changed.2 Release points change arm angles, and those in turn affect platoon splits, or how well a pitcher does against batters of different handedness. Sideways arm angles — the product of low release points — establish more horizontal movement, which can befuddle same-handed batters. Typically, pitchers perform better against same-handed batters, and before the 2013 season, Arrieta was no exception. But as his release point drifted upward, Arrieta, who is a right-hander, began to show a reverse split: For the past three years, he’s been better at getting lefties out than righties.

Beyond the modified platoon split, Arrieta’s new release seems to have allowed him to develop a consistency he didn’t have before. The standard deviation of Arrieta’s release is substantially narrower than average (meaning he was more consistent) in 2015 and 2014, after being wider than average in all his previous seasons. Release point consistency is correlated with walk rate, and along with Arrieta’s more steady release came a profound improvement in command, from 4.90 walks per nine in 2013 to 2.08 in 2015.

Arrieta’s release point evolution is extremely rare. In a given year, most pitchers sustain a game-to-game standard deviation in release point of only a single inch. (Think about that! Hundreds of times, pitchers perform a motion as violent as hurling a 95-mph fastball with a consistency of plus or minus a single inch!) Even from year to year, so practiced are their mechanics that pitchers vary their release points by merely 1.8 inches on average.3

Arrieta is a different story. His largest single-year change (from 2012 to 2013) ranks in the 90th percentile of all players’ single-year changes since 2009.4 Arrieta’s ongoing trend toward a higher and farther-right release point is even more impressive over a longer time period. Over any two years between 2009 and 2015, Arrieta’s release point change is in the 95th percentile; over three, only 13 pitchers made larger changes to their release point. Over four years, only eight pitchers5 experienced as much release point movement as Arrieta did.

Those eight pitchers are very different from Arrieta. Many are pitchers who have suffered extensive injuries since 2010, including Brandon McCarthy (missed 417 days), Clay Buchholz (306), J.A. Happ (235) and Tommy Hanson (238).6 The only pitcher on the list who has missed fewer days since 2010 than Arrieta (161) is Cole Hamels (101), but Hamels was already an established frontline starter in 2010. His evolution since then has been more about coping with the normal effects of age, as opposed to growing into an ace, as Arrieta has.

Perhaps the best parallel for Arrieta is Blue Jays pitcher Marco Estrada, who missed 222 days. Like Arrieta, Estrada seems to have embarked upon a program of steadily moving his release upward, becoming more of an over-the-top arm slot. But unlike Arrieta, Estrada — who is also a right-hander — has moved toward the center of the rubber and away from third base. Whether that choice is at all related to Estrada’s lack of success (his 3.31 ERA and 4.50 FIP in 2015 are uninspiring) is an interesting question. Maybe, like 2013 Arrieta, Estrada is only a few inches of release point away from becoming an ace.

What makes Arrieta unique is not that he changed as much as he did — it’s that the changes were associated with such a drastic improvement. Most of the time, a release point transformation like Arrieta’s is the product of injury. But in Chicago, Arrieta didn’t just change; he adapted into one of the best pitchers in the league.

Footnotes

  1. Here, I’m using Baseball Prospectus’s version of pitcher WAR, which is based on its new pitching statistic Deserved Run Average.

  2. It’s popular to attribute the change to Cubs pitching coach Chris Bosio, who has had success in developing other pitchers, but it appears as though Arrieta began his transformation long before getting to Chicago.

  3. For these calculations, I used Pitch Info’s corrected release point coordinates, which adjust for calibration errors between parks.

  4. I got that stat after z-score normalizing the average horizontal and vertical coordinates for each pitcher, in each year since 2009. I limited my analysis to pitchers who threw more than 1,250 pitches per season, eliminating relievers and partial seasons. That was done to ensure that the other pitchers in the data set could be fairly compared with Arrieta.

  5. Out of the 203 pitcher-spans that qualified.

  6. All data on days missed comes courtesy of Baseball Prospectus, in particular Corey Dawkins’s manually curated injury database.

Rob Arthur is FiveThirtyEight’s baseball columnist and also writes about crime.

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