Why Can't Jake Arrieta Strike Anybody Out Anymore?

It wasn't long ago when Jake Arrieta was one of baseball's premiere strikeout artists. Now, he has one of the game's lowest K rates. What happened?

No player better illustrated the immediate change in the way front offices approached free agency this offseason than Jake Arrieta. After winning a Cy Young award and a World Series in four-and-a-half standout seasons with the Cubs, Arrieta hit free agency for the first time in his career. His own team barely made an effort to sign him, and a slow market held back by Shohei Ohtani and Yu Darvish further complicated matters. Arrieta had little traction until March before finally signing with the Phillies just about two weeks before Opening Day.

Given how late Arrieta signed, it wasn’t a surprise to see him start slowly. He allowed six runs, four earned in 10 2/3 innings across his first two outings of the year, which came against the Marlins and Rays, not exactly offensive powerhouses. What was more alarming was the fact that he had just six strikeouts in those two games. When he fanned 10 Pirates in his third start of the year, he appeared to be back to normal. It turned out to be a mirage.

That 10-strikeout start, once the norm for Arrieta, is the outlier this season. He has just 19 strikeouts in 33 2/3 innings since then, a stretch covering six starts. Seven of those strikeouts came in his win over the Braves on Wednesday. Arrieta’s strikeout rate is down to 17%, barely more than half of what it was when he won the Cy Young in 2015. He has two or fewer strikeouts in five of his nine outings this season. He had four during his entire Cubs tenure, none of which came between June 4, 2014, and September 20, 2017. Once one of the league’s premier strikeout artists, Arrieta is ranked 81st among 92 qualified pitchers this year in strikeout rate, sandwiched between Trevor Williams and Aaron Sanchez. Not only is he no longer missing bats, but his walk rate is still prohibitive, checking in at 8.3% thus far this season. What happened?

To answer that, we have to go back to Arrieta’s dominant 2015 campaign. That year, he put together one of the greatest half-seasons in MLB history, totaling a 0.75 ERA, 0.73 WHIP and 113 strikeouts in 107 1/3 innings after the All-Star break. With two different fastballs that sat 94-95 mph, a confounding slider/cutter combo, and a filthy curveball, Arrieta became expert at getting hitters to chase pitches out of the zone. He had a 33% o-swing rate, the frequency with which hitters swing at pitches out of the strike zone, which ranked 23rd in the majors. What’s more, they made contact on just 59.5% of those swings, also 23rd in the league. Combine that with the nastiness of Arrieta’s stuff, and you get plenty of whiffs and weak contact, exactly what carried him to the Cy Young that year.

One other trait about Arrieta’s 2015 jumps out, and lays the groundwork for his strikeout demise. Arrieta threw more pitches out of the strike zone than in it in 2015, yet had a walk rate of just 5.5%, good for 21st in the majors. In fact, he had the fifth-lowest walk rate for a pitcher who threw fewer than 48% of his pitches in the strike zone, behind only Madison Bumgarner, Chris Sale, Zack Greinke and Dan Haren.

OK, let’s start working our way to the present day. Arrieta was largely the same pitcher in 2016 that he was in 2015. There were no substantive differences in velocity, movement, pitch mix or mechanics, and yet, his strikeout rate fell to 23.9%, while his walk rate exploded, landing at 9.6%. He cut down on the walks last season, though he still issued free passes to 7.8% of the batters he faced, while his strikeout rate dipped further to 23.1%. While he did lose a bit of velocity last season, it wasn’t enough to make a dramatic difference. Everything else, from movement to usage rates to mechanics, remained the same.

The difference, then, wasn’t with Arrieta, but with the hitters. His o-swing rate in 2016 dropped to 31.3%, a loss of 1.7 percentage points from his Cy Young year. It took another tumble the next season, this time to 29%. Arrieta was doing largely the same things that won him a Cy Young and made him one of the most dominant pitchers in the league, but hitters had caught on to his act. Not only did they cut his strikeouts and increase his walks by laying off pitches out of the zone, but they forced him into high pitch counts with regularity, nearly eliminating his ability to pitch deep into games.

That issue has reached its pinnacle this season. Hitters have all but stopped swinging at Arrieta’s chase pitches, plunging his o-swing rate to 26.6%. That ranks 74th among qualified pitchers. Andrew Cashner and Ian Kennedy are getting hitters to chase pitches out of the zone more often than Arrieta. On top of that, hitters are making contact on a whopping 76.7% of Arrieta’s pitches out of the zone, the highest o-contact rate in the majors.

Additionally, Arrieta is throwing more pitches in the strike zone, 50.7% heading into Wednesday’s start against the Braves, than he has since 2013. Hitters are making contact on 90.5% of the pitches they swing at in the strike zone, the highest rate of his career, and 13th-highest in the majors, between Jhoulys Chacin and Brandon McCarthy. Three years ago, it would have seemed unthinkable that Arrieta would ever end up rubbing elbows with their ilk in a contact-rate stat, but here we are.

Take all that, mix in noticeably reduced velocity for the first time in Arrieta’s career, and you get his disappearing strikeout rate and still-ballooned walk rate. In fact, that he is throwing more pitches in the zone than ever and has still walked 8.9% of the batters he has faced further illustrates just how often he’s getting hitters to chase his pitches out of the zone. Arrieta has been able to pitch around these deficiencies, totaling a 2.45 ERA and 1.15 WHIP in 51 1/3 innings this season, but his FIP is at 3.24, his xFIP is 4.02 and his SIERA is 4.31. The bet here is that Arrieta cannot survive this combination of strikeout dearth and walk abundance much longer.