Michael Kopech’s slider isn’t bad, but it needs some re-shaping

Staff report


Kopech’s slider isn’t bad, but it needs some re-shaping originally appeared on NBC Sports Chicago

It’s been a tale of two different seasons for Michael Kopech, and due to the knee injury he suffered in mid-June, we’ve been provided an easy place to split the season up.

  • April – June 12: 51.2 IP, 1.92 ERA, 3.10 FIP, 25.2 K%, 11.9 BB%, .136 BAA

  • June 19 – Sept 13: 67.2 IP, 5.19 ERA, 5.57 FIP, 18.5 K%, 11.3 BB%, .241 BAA

Even if you use the mantra of “ERA tends towards a player’s FIP,” even the most pessimistic of estimators didn’t see the drop-off in Kopech’s season to where it’s been recently. He’s struggled with the home run ball (from 2.9% HR/FB pre-June 19 to 14.3% HR/FB since June 19), and a decrease in fastball velocity from an average of 95.4 mph to 94.5 mph has placed extra pressure on both Kopech’s command and offspeed pitches. The nearly similar 11% walk rates leave plenty to be desired, which places the emphasis solely on Kopech’s offspeed pitches. While he does feature a curveball that he throws about 10% of the time, his main offspeed pitch – which he throws about 27% of the time – is his slider.

Michael Kopech’s 2021 slider, by all accounts, was a “plus” pitch. With a 36% Whiff Rate, he found himself in a position to build and even lean on his slider while his other pitches continued to develop.

…Except, this season, we haven’t really seen that same slider, and should Kopech want to remain effective, he’s going to need to make some changes.

In order to get an understanding of why Kopech’s slider needs some improvements, it’s important to understand how the pitch has changed year over year. When observing the statistical results on his slider from 2021 to 2022, the differences are clear – though, at first glance, can partially be chalked up to a pitcher learning how to be a starter while battling a knee injury.

It’s the spin and whiff rate numbers, however, that really raise an eyebrow and start to tell the story of what has changed this season.






















Usually, a change of about 100 RPMs in spin rate is nothing to sound alarm bells over. However, when it’s accompanied by a drastic drop in whiff rate and worse results, it signals a change in: (a) how the pitch is moving, (b) how batters are viewing it, or (c) a combination of both.

Just a cursory glance at Kopech’s curveball from 2021 to 2022 shows a pitch that has lost some of its horizontal movement without making up for it via increased vertical movement.

October 2021 

August 2022

The still frame images, while not perfectly from the same angle, show pitches that start in two completely different places, only to end up in (relatively) the same position. The 2021 Kopech slider starts well within the zone and carries out of the zone. The 2022 slider hangs around the outside corner and falls out of the zone.

October 2021 

August 2022

While these aren’t necessarily Kopech’s two best sliders, the numbers back up what the video shows: it’s the curious case of Michael Kopech and the two different sliders.

Read more about how Kopech’s slider has changed this year and what he can do to return to form over on soxon35th.com.

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