The Seattle Mariners have a strong bullpen heading to the 2023 season. One interesting thing about it is that there are two unique sliders being utilized: the gyro-slider and the sweeping slider. The gyro-slider was seemingly taught to two of the relievers after they were traded to the Mariners. The sweeping slider is utilized by two relievers who were in the Mariners’ minor league system before making their MLB debut.

In this post, we will explore the two different types of sliders, and see how effective they are for each pitcher who throws them.

The Gyro-Slider

RHP Andrés Muñoz and RHP Diego Castillo were both acquired by the Mariners via trade in 2020 and 2021, respectively. Since joining the team, both pitchers have adjusted their pitch usage and made similar alterations to the shape of their sliders. Their current slider is a hard slider with tight movement, which we will refer to as a gyro-slider.  

A ‘typical’ slider sits at about 84-mph and exhibits a sweeping motion. Gyro-sliders are considered to have ‘below average’ movement, which is often because they are thrown harder and therefore do not generate as much horizontal movement (sweep) as a slower version of the pitch. But just because they have below average movement, that doesn’t mean they can’t still be used as weapons.

Andrés Muñoz’s Gyro Slider

Andrés Muñoz joined the team in 2020 but did not get the opportunity to pitch consistently until 2022, after he recovered from Tommy John surgery. His two primary pitches were always fourseam and a slider. After joining the Mariners, his pitch usage took a complete 180:

Not only did his pitch mix change, but the profile of his slider changed as well. Previously throwing the slider 86-mph on average, Muñoz threw it 88-mph on average in 2022.

With the Padres, Muñoz’s slider had above average sweep and was considered to have an ‘above average’ movement profile. Since he joined the Mariners, his slider shape has changed, and now has below average sweep. While you’d typically like to see more movement on pitches, this slider has been an incredibly successful pitch in 2022 and helped turn Muñoz into a top end reliever. Check out the differences in results:

That’s nearly a 2-run difference in ERA. So despite having below average movement on the pitch, Muñoz is still getting elite results.

Here is the improved pitch:

Diego Castillo’s Gyro-Slider

Diego Castillo has a similar story. When Castillo was with the Tampa Bay Rays, his slider had above average sweep and depth. After being traded, Castillo added 2-mph to his slider (bringing it to 88-mph on average) and changed the movement profile. His new slider has below average sweep and depth.

The slider performs very close to MLB average overall:

While the results are not as strong as Muñoz’s, Castillo is a pitcher with historically below average control and command. That, in part, is contributing to the results of the pitch not being as elite as Muñoz’s. Regardless, the pitch is still performing slightly better than league average.

Check it out below:

The gyro-slider is more often utilized by pitchers who throw harder, so it is not surprising that Muñoz (fastball velo: 100-mph) and Castillo (fastball velo: 95mph) are both using one. The more interesting part to me it that they both already had sliders in their arsenal that exhibited above average sweep but opted to reduce the movement in favor of a 2-mph increase in velocity.

While having more velocity is great, it does not always outweigh the reduction in movement. While it certainly did for Muñoz, Castillo has had different results:

Increasing the velocity and changing the movement from above average to below average on the slider has led Castillo to get worse results from the pitch compared to when he was with the Rays. The pitch is results in more damage (higher xSLG) and is not getting as much swing and miss when thrown in-zone, despite him throwing it in-zone 6% more frequently with the Mariners.

The Sweeping Slider

RHP Matt Festa and RHP Matt Brash were both prospects in the Mariners’ system before making their MLB debuts. In contrast to Muñoz and Castillo, Festa and Brash have a sweeping slider in their arsenals.

Sweeping sliders have even more sweep than a ‘typical’ slider, and their horizontal movement resembles that of a frisbee. Sweeping sliders are typically thrown on the slower side (80-83-mph), but there are cases where pitchers can still get a similar movement profile while throwing the pitch harder.

Matt Festa’s Sweeping Slider

Matt Festa was signed by the Mariners in 2016 and was promoted to the Majors for his first full season in 2021. He throws a 83-mph slider and a 93-mph fastball, with the slider being his primary pitch. At 83-mph, his slider is a lot slower than that of Muñoz and Castillo, but it is still an effective pitch.

Festa’s slider gets over 6-in more sweep than MLB average, according to Baseball Savant. Here’s how the pitch performed compared to MLB average in 2022:

Festa’s slider performed very close to an average MLB slider in 2022. Check it out below:

Matt Brash’s Sweeping Slider

Matt Brash was traded to the Mariners in 2020 and made his MLB debut in 2021. He is also a slider first pitcher, but his velocity falls more in line with Muñoz and Castillo than Festa, with the average velocity on his fastball at 97-mph.

Even though his slider is harder than average (87-mph), Brash throws a slider that is more like Festa’s.

Brash’s slider gets close to 10-in more sweep than MLB average (which is incredible movement, especially given the velocity). Here are the results:

The expected weighted on-base average (xwOBA) of Brash’s slider is significantly better than MLB average. Check out the pitch below:

Both Festa and Brash’s sweeping sliders are successful pitches and performed close to or above MLB average.

Conclusion

The gryo-sliders and sweeping sliders in the Mariners’ bullpen will all be difficult pitches for opposing hitters to do damage against this season. The most valuable part of having these two different sliders is that hitters cannot settle in to face just one slider movement profile. They will be forced to adapt to each pitcher’s arsenal as they face them.

Overall, I think the differences in movement profiles demonstrates that even though one type of pitch might be working well for one pitcher, it doesn’t mean that’s the best version of the pitch for another. Even if the movement a pitcher already has is traditionally considered to be ‘above average’, there may still be a higher ceiling, even if it means going against traditional ideas to get there.