The Cubs’ Season Depends on Jake Arrieta’s Slider

It says something when a pitcher wins 18 games, records a 3.10 ERA, and people are still left wondering what went wrong. Nevertheless, that’s the case for Jake Arrieta and his 2016 season. Because he’s almost cut his slider usage in half this year — and because that alteration coincided with less dominant results than his 2015 campaign — much of the discourse settles on that pitch. His manager even admitted to wondering about it: “The break on the slider/cutter/whatever you want to call it has been more inconsistent,” Joe Maddon said after a poor outing by Arrieta in July.

The Cubs need Arrieta to find his slider tonight in Game Six in order to force this World Series to continue. By one metric — usage — the righty has returned to normal with the pitch. But has he really found it again? To answer the question, we first we need to figure out what he lacked this season relative to last; then we can see if things have returned to normal in the meantime. We’ll break the pitch down by three components: velocity, movement, and command.

Velocity
It’s tempting to point to velocity as the problem. Arrieta has lost a mile per hour on his slider from last year, and velocity is the most important aspect of a slider when it comes to whiffs. Case closed.

Except! Arrieta was up a tick on the fastball and the slider in 2015. Arrieta lost that tick, but he returned to the same velocity that he possessed in 2014, when he posted a 2.53 ERA and broke out with the Cubs. He struck out a batter more per nine innings in 2014, too, so it’s not just ERA that indicates Arrieta has been effective with an 89 mph slider.

And look, it’s still the third-fastest slider in baseball, behind only those thrown by Noah Syndergaard and Stephen Strasburg among starting pitchers. Yet, Arrieta has lost almost 20% of the whiffs on his slider, and gone from above average on the pitch to below average, and from throwing it more than all but five pitchers in the game to throwing it at a league-average rate. So perhaps velocity is part of it, but it doesn’t seem to provide a complete explanation.

Movement
Looking at overall movement for the slider seems like a good move, but the problem is that Arrieta essentially has two versions of the pitch: a harder, straighter cutter-type version and also a slightly slower, bigger-breaking version. This is totally intentional: “I can manipulate the velocity, I can manipulate the break, depending on the situation, depending on the hitter, depending on the count,” he told me about his breaking pitch in spring training of 2015. You can see the cutter on the left and the bigger slider on the right:

What we know is that the slider, on average, has actually featured almost a half-inch of additional drop this year. What that actually means in the context of this pitch, in particular, is probably that he’s having trouble with one of the two pitches that we call his slider.

The whiff rate is down on the slider in general, we’ve established that. But it’s decreased more substantially on the “cutter” version rather than the “slider” one — if we can treat the two pitches as clearly different for the moment. Previously, he’d recorded a whiff rate of 13.2% on his cutter — defined as any breaking pitch with cutter-like drop or less. This year, that’s down to 11.0%, which represents a bigger drop than he’s experienced on pitches with more slider-like drop (down to 13.8% from 15.4%). He’s also using the pitch less: that harder pitch used to make up 53% of his sliders, now it’s down to 48%.

We also know that Arrieta’s release point is higher this year, and that release points can change movement on the pitch — as it has. Put that together with his usage and outcomes, and it looks like Arrieta lost the harder version of his slider this season. He’s actually lost his cutter.

Command
Moving release points, changing movement — of course command is going to be affected. Arrieta used to have command issues, walking four batters per nine until his breakout in 2014. He walked half as many in 2014 and 2015 combined, but then produced a more regressed towards his previous levels this year. Maybe this is an old problem coming home to roost.

Except that Arrieta made wholesale changes to his delivery and to his body, focusing on repeatability and athleticism. That delivery is largely the same, other than the release-point change, and yet his slider has seen a fairly drastic change in effectiveness, causing him to become more predictable and rely on the sinker more often.

How about slider command as a subset? Maybe he’s just lost that one pitch. There’s some evidence that he’s lost the command on the slider a bit, even to righties. Look at the chart on the left, from his breakout 2014-2015 run, how he used to fill up the low-and-away area strike zone. Now look at 2016 on the right and see how he’s missing low more often this year, and also not dotting that corner.

Arrieta sliders to righties, 2014-2015 (left), 2016 (right). Source: BaseballSavant.mlb.com

But there’s more — and it might get at why he’s lost the pitch. Take a look at where he’s putting his sliders to lefties in 2016 compared to the breakout two years. He’s not throwing that cutter on their hands as much, and has focused on the more slider-like one to their back foot.

Arrieta sliders to lefties, 2014-2015 (left), 2016 (right). Source: BaseballSavant.mlb.com

We’ve got the story here, finally. Arrieta has stopped throwing the cutter version of his slider as much, perhaps because it hasn’t been as effective with the velocity loss. That has led to relatively more usage of a bigger slider with more drop, and he might be having trouble spotting that bigger slider on the outside corner to righties. That’s why lefties are hitting the slider harder (isolated slugging is up nearly 100 points) — since lefties enjoy sliders more than cutters, generally — but righties are also having a better time against the pitch, simply by taking it off the corner for a ball.

Can he get it back?
Here’s the good news for Cubs fans: Arrieta has upped his slider usage to 30% in the playoffs, back to where it was when he was winning personal hardware — and a lot of it has come from throwing the cutter-type pitch more, especially to lefties. Take a look at that missing spot on the hands against lefties — it’s back in the playoffs.

Arrieta sliders to lefties, 2016 playoffs. Source: BaseballSavant.mlb.com

The bad news is that the whiffs aren’t all the way back, perhaps because the velocity is down even more after a long season, or perhaps because he hasn’t yet mastered the command on the bigger slider just yet.

Still, just showing confidence in the cutter is a good sign. It looks like he lost that cutter for a bit, and it hurt his slider, but at least he’s got both pitches back in his quiver. The Cubs’ season depends largely on that pitch — really, those pitches — right now.