Jake Arrieta: Great Again?

Last Friday, Jake Arrieta rode an effective “slutter” to another quality start, lowering his ERA to 3.63, and earning a victory over the visiting Blue Jays. His six strikeouts, two walks, six hits allowed, and one run allowed over 6 ⅔ innings lengthened a solid streak of quality starts to seven games, and he is currently pitching better than anyone else in the rotation, and perhaps the whole pitching staff, except perhaps his fellow large Texan, John Lackey. That’s good news, since Jose Quintana is struggling, Jon Lester is on the DL, and the bullpen is struggling to find its footing among injuries and ineffectiveness of key relievers. Arrieta is good again, at least temporarily, and that’s great news for both the Cubs, who will need a third playoff starter behind the aforementioned lefties Lester and Quintana, and for Arrieta, who is entering an offseason in which he’s hoping to score a big contract.

Has Arrieta truly improved aspects of his pitching, though? Has he tweaked or fixed his mechanics, added velocity to his fastball, altered his pitch selection, or found some command? If the answer to those questions is “no,” then the Cubs will be disappointed in Arrieta’s playoff potential and Arrieta’s 2018 team might be disappointed in his production. My hunch is that yes, Arrieta has made tangible improvements since the beginning of July, and that his effectiveness is not an illusion.

First, a quick overview of Arrieta’s stats this season, compared to his very good 2016. His ERA is half a run higher than last year’s 3.10; his 3.96 FIP is also half a run higher than last year; his DRA is over four for the first time as a Cub, a 13 percent better-than-average 4.14; and he’s striking out hitters at almost an identical rate to last year. Keep in mind, Arrieta’s 2016 was worse than both his 2014 and 2015 years, when he was one of the two or three best pitchers on the planet. He’s walking fewer hitters than last year—a solid 7.7 percent that’s better than his career average. Hitters are hitting for a higher average than in any of the last three seasons, and his BABIP is back around the mark it was in 2014 after two seasons of benefitting from a historically good defense. Perhaps most importantly, he’s getting fewer groundballs and more flyballs than he did from 2014-2016, 46.0 percent and 33.5 percent, respectively, and more of those flyballs are turning into home runs—a league-wide trend, of course.

So, Jake’s 2017 overall has been markedly worse than his recent soaring peak. We know that Arrieta’s velocity has been down this year, and that has manifested in a higher pull percentage (40.4 percent) on batted balls than from 2014-2016 and over his career, and harder contact. After an August when his fastball velocity dipped to its lowest for his whole career, his four August starts featured him throwing hard again. His 93.4 average this month is closer to his 94-95 marks over the past few years, and an improvement on his 92-ish average this year. His sinker still sits around 92, worse than recent history, but his changeup and slider are hitting 88 after being a down mile-per-hour or two.

The velocity bumps are encouraging signs, and there are some tangible changes in those pitches’ movements as a result. There is a widening gap in the vertical and horizontal movement of his four-seamer and sinker, differentiating the pitches more than they have been in the past. His slider is a bit stiffer and harder, with vertical movement closer to his 2015 when he rode that pitch to a Cy Young than the farther-dropping version of 2016. He’s perhaps manipulating his breaking pitches a bit more than usual, as Brooks Baseball’s slider and curveball denominations have both drifted from their other 2017 monthly marks. I’ve bolded and italicized the key trend in the following charts, showing consistency in horizontal movement but a widening gap in vertical movement between his breaking balls.

Horizontal Movement, 2017

April May June July August
Sinker -8.21 -8.07 -8.36 -8.47 -8.21
Slider 3.85 3.39 2.81 2.37 2.22
Curve 8.23 8.09 7.31 6.58 7.61


Vertical Movement, 2017

April May June July August
Sinker -19.17 -19.32 -20.11 -20.06 -20.49
Slider -30.81 -27.92 -29.05 -26.75 -25.81
Curve -54.88 -51.14 -50.67 -49.55 -49.11

The velocity and movement changes have paid off for the hirsute righty, as he’s seen his whiff percentage on his slider jump to over 20 percent, more in line with that dominant 2015 than the past year and a half. His changeup is seeing a few more swings and misses as well. In terms of how he has used those pitches, he’s made minor changes as well: he has rarely thrown his four-seam fastball, favoring the sinker and throwing more sliders than he has since May. His whiffs per swing on his three key pitches (sinker, slider, change) are higher than they have been for most of the year. It’s a wholesale shift in the character and relationship of his pitches, and Arrieta has reaped the benefits.

A week ago, Carrie Muskat quoted Joe Maddon on Arrieta: “Fastball command… His velocity is ticking up, command is back, slider is back. The stuff is more familiar right now.” Arrieta himself has claimed that his mechanics have been more in line with those that give him success, as his crossfire action often falters. Video of his July starts compared to video of his August starts reveals a slightly more forceful finish to Arrieta’s windup, which lines up with Arrieta’s comments about staying on reaching back more and staying on top of the ball.

Arrieta’s velocity, movement, and mechanics are on the up and up, and the results have followed, but there’s another perspective on his pitching that is necessary for understanding his last two seasons. Arrieta has both altered his preferred pitch sequencing and his ability to tunnel those pitches (i.e. make them appear the same at the batter’s crucial decision point in the ball’s path to the plate). While Arrieta’s most common pitch pairing is consecutive sinkers, last year his sinker and slider appeared more in tandem than his sinker and curve. This year, that is reversed, as he’s favored his sinker followed by his curveball. Importantly, Arrieta’s release and tunnel points on his consecutive sinkers have been slightly improved this year—both a bit closer together—and his sinker-slider has seen a similar trend, even more significantly. His curveball is looking more different than his sinker this year, and that is in line with the movement data cited above. An increase in deceitfulness could be an element of Arrieta’s recent success, and is concordant with the data we have about his movement, sequencing, and tunneling.

Will Jake Arrieta pitch great in September and lead the Cubs to the playoffs once again? That, I can’t answer. But the right-hander is looking more dominant than he has all season, and he has derived his results from a few changes that are discrete and sustainable if Arrieta stays healthy. May he ride his slider/cutter into October once more.

Lead photo courtesy Caylor Arnold—USA Today Sports

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1 comment on “Jake Arrieta: Great Again?”


Jake gave the game away. It’s attatude /poor.

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