What's Really Wrong with Jake Arrieta's Slider

Jake Arrieta's slider was better in 2015. While his slider saved 23.8 more runs than league average last year, the pitch has cost the Cubs 1.8 runs this year.  Jeff Sullivan of Fangraphs theorized that Arrieta's slider isn't as useful nowadays because of its higher release point. Having a higher release point, Sullivan said, might explain why Arrieta is throwing more sliders at the shins instead of the knees. Indeed, Arrieta has thrown 32% of his sliders no more than 18 inches above the ground, nearly double his 18% rate in 2015. But simply saying that a slightly higher release point -- a tenth of an inch -- is the root cause of his slider's ineffectiveness might be too simple of an explanation.


Is Jake Arrieta having problems with his slider because of a higher release point, like Sullivan suggested? Or can something else explain why Arrieta's slider has sucked?

Counter-argument to Sullivan

Sullivan used a month-to-month graph to illustrate that Arrieta's release point is higher in 2016 than 2015.

The chart looks convincing, doesn't it? But what does his game-to-game release points look like? 

His game-to-game data looks different than the month-to-month data. You can actually see how Arrieta's release point game-to-game was up and down during the later part of the 2015 campaign. In fact, there were several starts in 2015 where Arrieta had virtually identical release points to his 2016 starts. While the month-to-month difference looks different, the data is skewed by the game-to-game ups and downs. In actuality, his release points aren't drastically different and might not be the problem.

The actual release point location isn't the problem. 

What's truly different from 2015 is the in-game release point consistency. He was letting go of the baseball at a consistent location more so last year than this year.

I compared the difference between Arrieta's 2015 and 2016 in-game slider release points. I found a statistically significant difference between the years. In 2015, his release point varied by 0.06 inches in-game. In 2016, his release point has varied by 0.9 inches in-game. (p=0.002)

And get ready for this...

Arrieta's 2016 in-game inconsistent release point is mildly associated with less slider movement (Spearman R=-0.403; p=0.046)! In other words, his inability to let go of the baseball in the same spot might (not cause) be influencing his slider's cutting action. Maybe this is why he has been throwing sliders half an inch flatter in the last three months compared to 2015? Maybe. 


Arrieta's slider release point location might not be the problem; the consistency of where he lets go of the pitch could be the problem. His slider release point is about 0.3 inches more inconsistent this year, and the inconsistency is mildly associated with less slider movement. Compared to 2015, he's thrown sliders with half an inch less cutting action during the last three months. 

Arrieta might not need to actually change his release point. Instead, he might need to find a groove that allows him to be more consistent. 
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Friday Notes

  • Jeimer Candelario has a .402 wOBA in Iowa (257 PA).

  • Eloy Jimenez has a .417 wOBA in A ball (452 PA).  

  • Gleyber Torres has a .319 wOBA since joining the Yankees A+ affiliate. 
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Thursday Notes

  • Addison Russell's contact rate is 2 points higher than last year (71% vs. 73%). 

  • ZiPS projected Baez to have a .322 wOBA at year's start, and he currently has a .320 wOBA. 

  • Kris Bryant has a .407 wOBA, a substantial increase from his .371 wOBA last year, despite currently having a BABIP that is 35 points power (.378 BABIP vs. .348 BABIP). 
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Mike Montgomery's Secondary Pitches Are Top-Tier

Mike Montgomery will make his first start for the Cubs tonight. Montgomery has particularly thrived as a reliever this year, going into his start with a 2.43 ERA and 3.33 FIP, both of which influenced by an 8.45 K/9, 2.94 BB/9, and 58.2% grounder rate. While the Cubs will be using him exclusively as a reliever come playoff time, his next few starts could be an audition for 2017.

Relievers are different animals than starters, though. If the Cubs want to use Montgomery as a starter, he will need a deep pitch arsenal in order to get through the batting order multiple times.

Encouragingly, Montgomery has showcased a deep pitch selection as a reliever, having thrown a fourseam (41.01%), sinker (15.99%), cutter (12.01%), curve (21.95%), and change (9.03%) out of the bullpen. Throwing pitches that move to different sides of the plate (e.g., sinker vs. cutter; change vs. cutter; curve vs. cutter), in theory, should permit Montgomery to avoid platoon splits. Indeed, righties have only hit to a .294 wOBA off of Montgomery this year.

The best part about Montgomery's arsenal is that he has multiple pitches with high whiff rates.

We created a z-score/percentile calculator for pitch type swinging strike rate (swstrike%), going as far back as 2012. Swinging strike rates can be found on Swstrike% percentiles are useful when comparing the effectiveness of individual pitches. Most successful pitchers have multiple pitches with high a swstrike%.

Montgomery's change, curve, and cutter rank in the top tier of MLB lefty relievers for swstrike%. Having three pitches -- and three pitches used frequently -- that generate at least 77% more whiffs than the competition is impressive. While his fourseam and sinker don't make batters whiff as much as his other three pitches, his fourseam and sinker generate an above average amount of grounders (54% and 66% respectively).

I can't help but be giddy about Montgomery's future as a starter. I truly think he has the stuff needed to be successful. Nevertheless, forecasting Montgomery's potential for success is limited because he has not been exposed to the same batters over and over again like starters. Still, the data is encouraging, but like any stat, use caution in interpretation.

Picture from
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Wednesday Notes

  • Kyle Hendricks' 4seam swstrike% is 15% in August, nearly 2.5x that of his previous monthly rates.

  • Addison Russell is on pace for 23 homers this year, according to ZiPS rest of the season projections. 

  • Russell is also on pace to finish with +4 WAR.
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Tuesday Notes

  • Kris Bryant is projected to finish the year with an 8.0 WAR.  

  • Addison Russell's wOBA against lefties is .332 this year, a massive improvement from his .236 wOBA in 2015. 

  • Russell's contact rate since the All-Star Break has been 75.5%. 
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Cubs Related Podcast: The Kyle Hendricks Edition (August 23)

Doug and Brendan discuss Kyle Hendricks' basket of improvements (e.g., velocity, 4seam usage, 4seam whiff rates, etc.), Heyward and Soler's theoretical RF competition, Russell's improvements, and Bryant's MVP status.
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Monday Notes

  • Addison Russell's wOBA now stands at .329 after his two-dinger day in Colorado.  

  • Despite a 3.07 ERA, Hammel owns a less robust 4.27 FIP. 

  • Kris Bryant's 6.6 WAR is 3rd best in MLB and 1st in the NL. 
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