The best, most dominant pitch in MLB lives in the Mariners bullpen

Many of the most dominant closers in baseball history could attribute their success to one particularly potent pitch. Mariano Rivera is perhaps the most notable example, earning 652 saves and a postseason ERA of 0.70 while throwing his signature cutter almost 86 percent of the time.

More modern examples include Emmanuel Clase's power cutter, Jhoan Duran's splinker, Devin Williams' changeup, and Josh Hader's sinker. This year, Seattle Mariners closer Andrés Muñoz has risen to superstardom and maintained a perfect 0.00 ERA after 21.2 innings largely thanks to his slider.

Andrés Muñoz keeps throwing his slider because nobody in MLB can hit it

When his professional career started in 2016, Muñoz was mostly known for topping out in the triple digits on his fastball. However, realizing that velocity alone is rarely enough to succeed in the big leagues, the San Diego Padres noticed that his slider had the potential to be just as effective, if not more so. Thanks to San Diego's pitching development efforts, he began to rely on his slider more frequently and that has led him to where he is today.

In 2025, the pitch has been nigh untouchable. He has thrown it 49.1 percent of the time and it has a .047 batting average and a 53.4 whiff percentage. It has a total run value of plus-seven and its RV/100 of 4.4 places it third among all pitches in MLB. Each of the two ahead of him (Randy Vásquez's sinker and Luke Weaver's four-seamer) have been hit for higher averages and posted lower whiff rates.

The numbers on the radar gun are the most obvious aspect of Muñoz's pitching, but his ability to generate movement is what has elevated him to the next level. That's why it was all the more exciting when he started playing around with an off-speed pitch during spring training. He has only thrown this new "kick change" four times this season, so there's a good chance he's still working on finalizing the weapon. Even still, having another tool with arm-side movement could make his slider an even more uncomfortable experience for opposing hitters.

To say that Muñoz has been an important part of this year's Mariners roster would be a complete understatement. With a total of 2.0 rWAR, he is the second-most valuable member of this year's team behind Cal Raleigh. He is already worth as much as he was across all of the 2024 season.

None of this is really new to him, as he has a 2.22 ERA over his five seasons with Seattle. But it seems for the first time, he's finally getting the appropriate amount of attention from baseball fans outside of the Pacific Northwest.