A look at the most dominant pitch used by every Mariners reliever

Seattle relievers combined for a 3.48 ERA in 2023, the fourth-best of any team in MLB. Even after losing Paul Sewald, new names stepped up to the plate and brought the Mariners within a few games of reaching the postseason for a second year in a row. Between a group of pitchers that have been with the Mariners for a while, to diamonds that the front office has uncovered, it was a mixed bag. So, what led to this success?

Relievers don't need the same diverse arsenal that starters do. Rather than deploying a wide array of all types of pitches, the best relievers and closers often perfect just one or two pitches. Mariano Rivera built almost his whole legacy with his cutter. Devin Williams and his unique "airbender" pitch have made him an elite closer in today's game.

We already took a look at the best pitches that all of the Mariners starters had in 2023, and it's time to take a look at the guys who sit out behind the fence in Part 2. Heading into 2024, what dazzling pitches should we expect to see from each bullpen arm currently on the depth chart?

Andres Munoz - Slider

Usage: 48.6%
BA: .230
Whiff Rate: 48.3%
Strikeout Rate: 39.6%
Total Run Value: 3

Intrinsically, Munoz has a filthy slider. Averaging 88.4 mph with 30 inches of drop, it shouldn't be any surprise that opposing hitters whiff almost half the time and strike out almost 40% of the time. It was truly devastating in 2022, when he accumulated a whopping 20 run value over just 65 innings and had a .126 BA.

This year's slider had a batting average almost twice as high, driven by more frequent hard contact. Opposing teams may have spent more time scouting and he may have been affected by being promoted to the team's closer, but with a full offseason of preparation, this pitch should return to its former effectiveness.

Matt Brash - Slider

Usage: 50.5%
BA: .162
Whiff Rate: 48.5%
Strikeout Rate: 44.1%
Total Run Value: 15

Brash went from a somewhat shaky reliever in 2022 to a dominant force in 2023. Reducing his ERA from 4.44 to 3.06 was no easy task but with a new and improved slider, he became an anchor in the bullpen. This pitch averaged 88.8 mph, 31.4 inches of drop, and 11.8 inches of horizontal break.

While his slider is dominant, developing another plus-pitch (perhaps refining his slider?) would take him to a whole-nother level.

Gregory Santos - Slider

Usage: 52.6%
BA: .196
Whiff Rate: 37.5%
Strikeout Rate: 30.8%
Total Run Value: 17

The newest member of the pitching staff arrived from the White Sox in exchange for Prelander Berroa and Zach DeLoach. He was great in his first full major league season in 2023, posting a 3.39 ERA and is looking to be a promising arm. His style follows the theme, largely depending on a devastating slider that averaged 91.4 mph, 31 inches of drop, and 5.7 inches of horizontal break.

He'll be arbitration eligible in 2026 and a free agent in 2029, so assuming he's effective he might be a bullpen staple for the next several years.