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How the Slider has Improved Tyler Glasnow’s Game

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It’s not enough to simply add variety. It’s how Tyler Glasnow is using his new pitch that makes it so good.

MLB: Tampa Bay Rays at Boston Red Sox Brian Fluharty-USA TODAY Sports

Tyler Glasnow worked on adding a new pitch to his arsenal this offseason. The movement of the pitch is similar to that of a cutter and slider, which helped coin the name “slutter”. I will be referring to it as a slider, as that is how it is classified on Baseball Savant and Brooks Baseball. A little over one month into the season, how has it worked out so far?

Why Did Tyler Glasnow Need a Third Pitch?

In 2020, Tyler Glasnow had two primary pitches, a fourseam and a curveball. He also sprinkled in a change-up, throwing it about 3% of the time. Glasnow’s results were very good last year, as he was among the top of the league in terms of swing and miss, strikeout rates and velocity. But there is always room for improvement, and the introduction of the slider is allowing Glasnow to take his abilities to the next level.

There are three ways the slider makes Glasnow even tougher to face. It allows Glasnow to:

  1. Go deeper into games
  2. Utilize more of the strike zone
  3. Be less predictable

In 2020, Tyler Glasnow averaged 5.2 innings pitcher per start. So far this season, he is averaging 6.1 innings pitched per start. In a short sample size of eight starts, he’s already achieved that first goal.

By design, Glasnow is certainly utilizing more of the strike zone as well. Prior to the introduction of Glasnow’s slider, he divided his fourseam and curveball in the zone. He used his fourseam up in the zone, and his curveball low and below the zone.

The slider lands in the middle, east edge of the zone. This breaks up the two more extreme locations and prevents hitters from sitting on a pitch high or low.

Heat Maps
Baseball Savant

Looking into the movement of the three pitches, all three have above average vertical movement and below average horizontal movement when compared to those of similar pitchers. The pitch movement diagram below shows the differences in movement between Glasnow’s three primary pitches.

Pitch Movement Diagram
Baseball Savant

The slider also serves as a mid-level velocity pitch and breaks up the large velocity difference between that of the fastball and curveball (13 mph difference). The difference in movement paired with the difference in velocity makes it more difficult for hitters to:

  • Anticipate a certain pitch
  • Recognize it early in the release
  • Get their timing right

Being Less Predictable: How is he incorporating the slider?

Glasnow is throwing the slider 29% of the time, second most in frequency to his fourseam (53%). The biggest reduction in pitch frequency comes to his curveball, which was thrown 35% in 2020, but only 14% so far in 2021. The introduction of a third pitch that is being used as frequently as this slider allows Glasnow to be less predictable to hitters.

Let’s take a look at how Glasnow’s pitch usage has changed in key counts: first pitch and counts with two strikes.

First Pitch

First Pitch vs RHH and LHH
Data from Brooks Baseball

Against both left and right handed hitters, the first pitch is more evenly split between the fourseam and slider when compared to 2020.

Last season, Glasnow relied on his curveball first pitch between 20-30% of the time depending on whether he was facing a left or right handed hitter, but has pretty much stopped throwing it altogether first pitch this season. Likewise, he reduced the usage of his change-up first pitch.

With Two Strikes

Two Strikes vs RHH and LHH
Data from Brooks Baseball

In counts with two strikes, Glasnow has reduced the use of his curveball against both right and left handed hitters, and has mixed in the slider.

While not conveyed in the graph above, Glasnow has used his curveball as more of a chase pitch in 2021. He uses the curveball primarily when he is ahead in the count, and throws it low so it breaks below the zone and generates swing and miss.

How has the slider affected Glasnow’s results?

The addition of the slider has helped improve the results of his fourseam and curveball.

Results of Glasnow’s fourseam and curveball
Data from Baseball Savant

The opponent SLG on his fourseam and curveball dropped significantly. Glasnow is getting higher swing and miss on both pitches as well.

His strikeout rate remains the same, within the top 4% of the league. Flyballs still remain an issue for Glasnow, but hopefully he will see a reduction as Glasnow continues to develop his slider.

In terms of the results of the slider, the opponent SLG is on the higher side (.452), but it does have good swing and miss, at 40%.

Concluding Thoughts

The introduction of the slider may be what Glasnow needed to reach the next level of his potential. It is allowing him to be less predictable on the mound, deceive hitters, and is improving the results on his already established primary pitches.

I’m looking forward to how he continues to incorporate it going forward for many seasons to come.