Jake Arrieta may be the most important free agent pitcher this winter. He’s not the best pitcher available. At least by Dave Cameron’s criteria, that would be Yu Darvish. But he’s been good enough to likely earn a $100 million contract, and he’s shown signs of both brilliance and potential decline over the last two seasons such that a $100 million contract feels like it will be either $50 million too expensive or $50 million too cheap and nowhere in between.
Normally, I spend the bulk of these pitcher breakdowns looking for trends in strikeout and walk rates, and Arrieta is fertile ground for that analysis. The last two seasons, his strikeout rate is down about one per nine and his walk rate is up about one per nine from 2014-15. There are several potential sources for that decline. I would lean toward a loss of velocity and a decreased reliance on and effectiveness of his cutter as the likeliest culprits.
But rather than dive more deeply into that topic, I want to talk about Arrieta’s batted balls. That’s because, even while Arrieta’s strikeout and walk rates declined, he continued to limit the damage done by the balls put in play against him, in particular those hit on the ground. In his four and a half years with the Cubs, Arrieta allowed a microscopic .161 BABIP on his groundballs. The closest starter to him, Josh Tomlin, allowed a .185 BABIP on his groundballs, and only 8 other starters were below .200.
The highest groundball BABIP Arrieta ever allowed in a season with Chicago was .191 in 2014, and even that was nearly 50 points lower than the MLB average of .238 over that period. That’s a long track record of beating the regression odds, long enough that even most FIP-minded sabermetricians agree that Arrieta is responsible for that success by consistently inducing weak contact. That theory bears out in his hard contact rate on groundballs, which is also the lowest in baseball since 2013.
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There are even two other pitchers who appear on both lists, R.A. Dickey and Clayton Kershaw, which makes the cause-and-effect assumption even more believable. In fact, Dickey is the perfect comparable player. He throws a knuckleball, which induces weaker groundballs, which decreases his BABIP allowed on groundballs. Arrieta developed his cutter in 2013, which also induces weaker groundballs, which also decreases his BABIP allowed on groundballs. It’s a tidy narrative, but I fear that it overlooks an important advantage Arrieta has had that I believe has contributed to his success, which is the quality of his defensive infields.
In four of his five seasons with the Cubs, his infielders saved at least 20 runs over the course of the full season according to Defensive Runs Saved (DRS). Their one down year, 2014, was the same year that Arrieta allowed his team-high groundball BABIP of .191. Meanwhile, notice the big increase in the Orioles’ third-base DRS in 2013, the year Arrieta was traded mid-season. That was two-time Gold Glover Manny Machado’s first full season. With the addition of Machado, the Orioles had suddenly become a tremendous defensive infield, on par with many of Arrieta’s Cubs teams, and Arrieta actually saw his BABIP on groundballs plummet to .174 that half-season with the Orioles, which is on par to what he consistently saw with his new team.
Those 23.2 innings with the Orioles in 2013 were not much of a sample. Maybe that was all luck, and it was Cubs’ pitching coach Chris Bosio’s tweaks to Arrieta’s positioning on the rubber and mechanics that made his cutter what it is today, which started to induce the weaker contact, which was the real reason for Arrieta’s decreased BABIP allowed on groundballs. But I suspect the truth is somewhere in between, and Arrieta owes some real portion of his improvements with the Cubs to the defensive talent he had around him.
That theory is not one that if true would submarine Arrieta’s free agent value. It might actually be an encouraging sign that Arrieta could perform in front of any good defensive infield, not just the historically great one he had in Chicago in 2016. But since Arrieta provides so much of his value with the results of the batted balls he allows, I suspect he might be more susceptible to the defensive influences of whatever new team decides to sign him. For me to want to draft him next season, I’ll need that new team to have some glove guys in their infield.
Scott Spratt is a fantasy sports writer for FanGraphs and Pro Football Focus. He is a Sloan Sports Conference Research Paper Competition and FSWA award winner. Feel free to ask him questions on Twitter – @Scott_Spratt