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40 in 40: Andrés Muñoz is the answer

The 24-year-old flamethrower is the fiery heart of Los Bomberos.

Houston Astros v. Seattle Mariners Photo by Daniel Shirey/MLB Photos via Getty Images

When the Seattle Mariners first acquired Andrés Muñoz from the Padres he was easily the biggest unknown in the deal, still a long way off from returning from injury and with very little major league experience under his belt. In many ways, baseball is a sport of uncertainty, and of reading between the lines: of asking questions, and seeking answers. As the sport continues to evolve we’ve found more advanced ways of asking these questions, and of answering them. Yet for all the ways we have to track value, and predict it, we will always be left with some unknowns. There will always be what-ifs, uncertainties, and “could have been”. As much as we strive to predict the future of prospects and players at every level, and by extension the team, there is no clearer answer than when we finally get to see results. Nearly two and a half years removed from the deal that brought Muñoz to Seattle, and after a full year of play, he has answered many questions for us with his results.

American League Wild Card Series: Seattle Mariners v. Toronto Blue Jays Photo by Thomas Skrlj/MLB Photos via Getty Images

Who was the headliner of the deal that brought Andrés Muñoz to Seattle? Received from San Diego at the tail end of August in 2020 was Taylor Trammell, Ty France, Luis Torrens, and Andrés Muñoz. Now, I honestly think it’s a little silly to worry so much about who the best piece in a trade either is or will be, but it is still interesting to note how the thinking has evolved over time based on the results. Trammell, the highest-rated prospect of the group, was then thought to be the headliner, but still remains much of a question mark. Ty France has firmly slotted himself into the conversation, since then playing his way into everyday status and even earning an All-Star nod. Torrens, well, let’s just leave it at wishing him the best of luck on his minor league deal with the Cubs. But for Muñoz there is a strong argument that he either already is, or will definitively be, the biggest return in that deal, as some on this site predicted at the time.

What about the concerns at the time? The biggest concern with Muñoz from his minor league and early major league numbers pre-injury was his command, and by extension his high walk rate. It was proposed that maybe he would need to drop some of that staggering velocity in order to gain some command, and the Padres already had been working with him in mixing in his slider more to better complement the fastball. His results certainly improved, last year maintaining a high strikeout rate of 38.7% that against a career-low walk rate of 6% was good for a K-BB of 32.7%, or second-best among all major league relievers. He did this all without dropping velocity, his average velocity on his fastball actually going up from 99.9 mph in 2019 to an average of 100.2 (!) in 2022, behind only Jhoan Duran’s 100.8. His slider saw an even bigger uptick from 86.3 in ‘19 to 88.6 in ‘22. So what was the difference?

Muñoz’ 2019 heat map.
Baseball Savant

In 2019, over 23 innings, Muñoz leaned most heavily on his fastball by throwing it two-thirds of the time, leading with the fastball while using the slider primarily as a putaway pitch (but relying on the fastball to bail him out when he was behind in counts), but throwing neither with particularly good command. His fastball at the time had a whiff rate of 22.2%, and his slider a whiff rate of 46.8%. You can see how often the fastball leaked into the middle of the plate, where even with premium velocity MLB hitters were able to track it down. This resulted in an actual SLG of .472 against an xSLG of .535, and an above average number of barrels per plate appearance. The slider produced a large number of whiffs but was also located dangerously near the center of the plate.

And then, after injury-shortened seasons in 2020 and 2021...

Muñoz’ 2022 heat map.
Baseball Savant

In 2022, Muñoz completely flipped that script. The fastball is now the change-of-pace, setting up the slider that’s being thrown two-thirds of the time, and both with more consistent location. Muñoz now leans on the slider as a first pitch in an at-bat, and more often goes back to the slider when he’s behind in counts as well as for a strikeout pitch. While his whiff rate on the fastball has stayed exactly at 22.2%, the much trickier to hit slider has climbed some to 50.8%. What the Padres started the Mariners have further leaned into, taking advantage of what was Muñoz’s best pitch all along.

The velocity on the fastball of course is elite and has its use, but the pitch could still use some improvement. He did begin locating it much more ideally at the top of the zone, but the results last year were much in line with 2019, yielding an actual SLG of .500 and an xSLG of .399, and a whopping hard hit percentage of 54.9. It’s a relatively flat pitch, and with such a low whiff rate it is best used in its current form to set up the slider. It’s truly his slider that makes him one of the best in the league. But don’t take my word for it.

Nothing here to be blue about.
Baseball Savant

One look at his Baseball Savant page’s sliders make it pretty clear that Muñoz was elite in just about every category of results last year. He also was in the top rankings of relievers in many categories not pictured. His actual FIP of 2.04 was good for 9th best in the league of bullpen arms, and his perfectly matched xFIP of 2.04 was third best, and his xFIP- of 51 was second best. And while his actual ERA ranked 34th at 2.49, his xERA of 1.84 suggests that already great number was affected by some bad luck. His team best (out of relievers, third if you include the starters) 1.9 fWAR was tied for 6th best with Reynaldo López of the White Sox. So his overall results, in pretty much any way you slice it, were top tier. But what about the slider, specifically?

The best pitches in baseball, 2022.
Baseball Savant

Andrés Muñoz’s slider was tied for 6th best in all of baseball in terms of Run Value at -20, equal to Spencer Strider’s four-seamer. If we look at other places on that leaderboard you see that it also ranks high in many other categories as well. Out of the pitches shown, it ranks first in xBA and xwOBA, and second in xSLG just .001 behind Edwin Diaz’ slider, which is also the only pitch it trails on this list in whiff rate. It’s very encouraging to see the progress he has made and the results from his use of the slider as a primary pitch. Concerns about his health returning from injury were also set aside last season, his sixty-five innings pitched the second most in the reliever corps, a trend that will hopefully continue into next season. Something else to keep an eye out for in 2023 is if the Mariners pitching development works with him to possibly tweak his fastball to be even more effective, as the velocity alone isn’t generating the swing and miss you would hope to see.

In many ways, Muñoz has already answered some of the questions facing him, even exceeding some of the lofty expectations his peripherals allowed many to dream on his development path. But questions still remain. What will his presence mean for the club going forward? Can he continue last season’s success? Can he improve his fastball?

Given the trend of his development, and the positive outlook in next year’s projections systems with little variance between them, it stands to reason he can. As far as his fit with the club on the personality side of things, he is the originator of the bullpen nickname Los Bomberos, and his attitude and ambition are certainly easy to root for. As far as results on the field go, the Mariners have the young twenty-four-year-old locked up for the next several years on a deal that is so team-friendly as to be almost criminal.

There are still many questions in his future, in that of the Seattle Mariners. But for now, we can expect him to continue to be a phoenix risen from the ashes of injury, fighting fire with fire alongside his fellow Bomberos. For now, the answer is Andrés Muñoz.