Friday August 21st, 2015

Over the winter, the Cubs committed $155 million to Jon Lester to head their rotation, but after five straight sub-.500 seasons, they still appeared to be short of contention-quality starting pitching. Jake Arrieta has challenged that perception, essentially replicating last year's 25-start showing, out-pitching his more heralded teammate and emerging as the staff's ace. On Thursday night, he helped the Cubs halt a three-game losing streak via six shutout innings against the Braves, continuing a two-month stretch of sheer dominance.

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Though his postgame comments indicated that he was less than pleased that he didn't pitch deeper into the game, Arrieta didn't allow a single fly ball to the Braves, struck out seven and scattered four hits and one walk over the course of his 107 pitches. That's part of a larger trend: This year, the 29-year-old righty has generated a career-high 54.2% ground-ball rate, up from 49.2% last year and 43.0% from his 2010–13 stretch with the Orioles. Overall, his 2.30 ERA, 2.62 FIP and 168 innings all rank third in the NL; his 5.0 WAR is fourth, his 170 strikeouts are fifth and his 0.5 homers per nine is sixth. That performance has placed him on the periphery of the NL Cy Young discussion, in the company of Zack Greinke, Clayton Kershaw, Jacob deGrom and Max Scherzer.

In fact, Thursday's outing marked Arrieta's 12th quality start in a row (six or more innings, three or fewer runs), matching Kershaw and John Lackey (who’s scheduled to start for the Cardinals on Friday night) for the season's longest streak:

name team span gs ip era fip
Jake Arrieta Cubs 6/21–8/20 12 86 1.26 2.30
John Lackey Cardinals 6/15–8/15 12 85 2.12 3.81
Clayton Kershaw Dodgers 5/26–8/1 12 89 2/3 1.10 1.74
Carlos Martinez Cardinals 5/20–7/25 11 75 1/3 1.08 2.78
Zack Greinke Dodgers 6/7–7/31 10 73 1/3 0.86 2.23
Zack Greinke Dodgers 4/7–5/27 10 67 1.48 3.16
Mark Buehrle Blue Jays 6/3–7/21 9 65 1.52 3.08
Jose Quintana White Sox 5/30–7/12 9 60 2/3 2.82 3.38
Jordan Zimmermann Nationals 4/18–6/2 9 60 1/3 2.09 2.97

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A note on quality starts: The stat has its detractors, because as many a blowhard TV announcer will repeatedly tell you, the worst-case scenario yields a 4.50 ERA, but such outings generally account for only a small fraction of quality starts (8.5% this year). When pitchers have delivered a quality start this season, their collective ERA is a minuscule 1.85, and their teams have a winning percentage of .679—the equivalent of a 110–52 team. When they don't deliver a quality start, starters' ERAs are a collective 7.29. While those figures may sound extreme, they're right in line with historical trends.

The bigger issue for the stat is its conventional reliance upon earned runs and the distinction between those and unearned runs, but we’ll save that argument for another day. From here, it’s more revealing that among NL starters, Arrieta trails only Greinke in quality starts (21) and quality-start rate (84%) than the fact that he leads the NL in wins (15).

As you can see from the table, Arrieta has been particularly stellar during his streak, which began with a four-hit shutout of the Twins on June 21 and has also included four other scoreless outings as well as a two-hit, one-run complete game against the White Sox on July 12 via which he posted a season-high game score of 88. The last Cub with a longer streak of quality starts was Greg Maddux, who reeled off 14 straight in 1992, the year he won his first Cy Young; he also had a 14-game streak in '88. The only other Cubs with a streak as long as Arrieta's since World War II are Moe Drabowski ('57) and Mike Morgan ('92, overlapping that of Maddux).

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A fifth-round 2007 pick out of Texas Christian University, Arrieta was regarded well enough as a prospect to crack the lower half of the Baseball America and Baseball Prospectus top prospect lists in both 2009 and '10, but he struggled mightily to establish himself at the major league level. From 2010 until July 2, 2013, when he and Pedro Strop were traded from the Orioles to the Cubs for Scott Feldman and Steve Clevenger, he pitched to a 5.46 ERA and 4.72 FIP, struggling to keep the ball in the park (1.2 homers per nine) and with his command and control in general (4.0 walks, 1.7 strikeout-to-walk ratio). He never made more than 22 starts or threw more than 119 1/3 innings in a season for the O's, who kept bouncing him between Triple A Norfolk and the majors. Only in '11, when he set those workload highs, did he avoid getting farmed out, and that was because he underwent a season-ending elbow cleanup in August.

Including his nine-start, post-trade run with the Cubs in late 2013, Arrieta has posted a 2.58 ERA and 2.79 FIP since coming to Chicago, doubling his strikeout-to-walk ratio to 3.5 and cutting his home run rate by almost 60% to 0.5 per nine. The drop in his homer rate and the aforementioned rise in his ground-ball rate both owe much to the increasing use of his sinker and slider. Via the data at Brooks Baseball, here's his breakdown pre- and post-trade:

team fourseam sinker change slider curve
Orioles 30.1% 30.6% 8.2% 15.7% 15.4%
Cubs 15.6% 35.4% 4.6% 27.5% 16.9%

Where Arrieta was throwing about as many four-seamers as sinkers during his days with the Orioles, he’s now throwing the sinker 2.3 times as often as the heater and is throwing fewer fastballs in general, with his rate of sliders nearly doubling. With virtually all of his pitches, he's generating higher ground-ball rates and yielding lower batting averages and slugging percentages—dramatically lower, in some cases:

  orioles       cubs    
Fourseam .262 .432 34.2   .209 .307 44.8
Sinker .296 .453 48.9   .246 .354 54.6
Change .302 .535 50.5   .107 .161 40.5
Slider .224 .431 38.6   .194 .294 49.1
Curve .234 .344 59.2   .159 .270 58.0

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Add it up, and it's an impressive step forward, one that can't be dismissed as a fluke even given his plummeting batting average on balls in play (.299 as an Oriole, .261 as a Cub including .269 this year). Given that this is the first season in which Arrieta has qualified for the ERA title, it might be premature to anoint him as a true ace. But the numbers he's put up on the North Side testify to the fact that at the very least, the Cubs have found themselves another frontline pitcher—an inexpensive one at that, as Arrieta is making $3.63 million in his first year of arbitration eligibility and is under control through 2017.

Thanks in part to Arrieta’s strong work, the Cubs (68–51) now hold a four-game advantage over the Giants in the race for the NL’s second wild-card spot, which means it may not be long before the debate begins over which of Lester or Arrieta is called upon by Joe Maddon in the one-and-done game. Don’t be surprised if it’s not the more expensive pitcher.

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