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What Changed For Mason Miller That Has Made Him Elite?

Oakland Coliseum; CC by License 2.0

Mason Miller of the Oakland A’s has taken Major League Baseball by storm this season, coming out of the bullpen with an electric fastball reaching 103.7 mph and while striking out 56.7% of batters he’s faced so far. He is also yet to allow a single barrelled ball in his first 285 pitches this season, which is a remarkable feat when you consider the fact that the average MLB pitcher allows 7 in every 100 pitches thrown. He’s saved 8 games for the A’s, totaling nearly half of the A’s current total of 19 wins, and is rumored to be on the trading block at the deadline in July. However, the reason Miller’s dominance comes as such a surprise is because he wasn’t nearly this successful in his rookie season for the A’s last year, and, because Miller has been able to develop within an A’s organization that is famous for having the worst facilities, the worst farm system, and the cheapest owner who has continuously refused to spend any money to improve the latter. Miller’s story is that of an underdog who has overcome his surroundings to become successful in a place where few players are able to do so. I know everyone, including myself, loves a good underdog story, so I am going to break down how Mason Miller evolved into the monster he is now, through pitch design, changes in his arsenal and usage profile, as well as any other factors that have contributed to his meteoric and unprecedented rise to the top of the relief pitcher totem pole.

Let’s start with pitch design and compare how Miller is throwing the baseball in the 2024 season vs. the 2023 season. In 2023, Miller threw a Four-Seam Fastball, a Slider, and a Cutter, as well as a Changeup that he almost exclusively threw to lefties. This season however, he’s only thrown a Four-Seam and a Slider (he’s also thrown 2 changeups, both to lefties, but that’s not enough of a sample size to go off of), so we’ll only compare the Four-Seam and Slider since he threw them in both of his MLB seasons. Obviously, it is a huge deal that Miller stopped throwing his Cutter and Changeup, but we’ll save that for a bit later. Also, a quick note to any readers not fluent in Baseball Savant terminology, I will be comparing the vertical and horizontal movement of Mason Miller’s pitches to MLB average. How Baseball Savant does this is by taking the average number of inches of drop (vertical movement vs. gravity) or break (horizontal movement) for all pitches within 2 mph of velocity and 0.5 feet of extension of the pitch you are looking at in order to remove any bias towards slower pitches or pitches released farther from the plate which therefore have more time to move farther. Starting with the 2023 season, Miller’s Four-Seam that year averaged 11 inches of drop which was 1.2 inches more than average, which makes sense given that he released it with 1-2 o’clock tilt. His Four-Seam surprisingly lacked much extra arm side run with just 7.7 inches compared to an average of 7.6 inches, and because of this, the shape itself doesn’t blow me away. However, as always with Fastballs, velocity is king, and because Miller’s Four-Seam averaged 98.4 mph, it still was a very good pitch for him, with a run value of 0.8 per 100 thrown which is better than the league average. Miller’s Slider in 2023 had 39.2 inches of drop which is 3.6 more than league average, and had 8.4 inches of break which is 3.8 inches greater than average. Miller released his Slider at 8-9 o’clock tilt, creating a Slurve shape with similar amounts of vertical and horizontal movement. Much like Miller’s Four-Seam, the shape of his Slider isn’t very unique. However, unlike his Four-Seam, Miller’s Slider does have outstanding amounts of break, making it an effective pitch on the inner and outer thirds of the plate. This is reflected by the pitch’s run value, which is 1.4 per 100 thrown and is also above league average.

Now to compare that to Miller’s 2024 season so far, his Four-Seam has lost 1.1 inches of drop and gained 1.4 inches of break. This is peculiar because normally we see an increase in ride (meaning a decrease in drop) or break, but not both at the same time because adjustments in the tilt of the ball at release change the direction of the spin of the ball from more vertical to more horizontal or vice versa. The change we see in MIller’s Four-Seam is not due to an adjustment in tilt, but rather an increase in the spin efficiency of the pitch, leading to more movement overall because the gyro angle has been decreased at release. Miller also greatly increased the velocity of his Four-Seam, from an average of 98.3 to 100.9 mph, which leads us to believe that Miller could also have increased the spin rate of the pitch, another reason the total movement of the pitch could have increased as well. These changes accumulated to increase the value of the pitch tremendously, from a run value of 0.8 per 100 thrown in 2023 to a current run value of 2.0 in 2024 so far. Miller’s Slider lost half an inch of both drop and break between 2023 and 2024. However, the pitch gained almost 2 mph in that span just like his Four-Seam. This change in shape is quite minuscule, but just half an inch less drop on the pitch made it an extreme outlier for its velocity range, going from 3.6 to 5.2 more inches of drop than the average pitch within 2 mph of its velocity. This caused a huge increase in the run value of the pitch, going from 1.4 to 4.1. It is clear that both Miller’s Four-Seam and Slider saw major improvements over the off-season, both in velocity, and in shape. So now let’s dive into how and when Miller is using these pitches to be successful.


In 2023 righties saw Miller’s Four-Seam 59% of the time, his Slider 32% of the time, his Cutter 8% of the time, and his Changeup just 1% of the time. Miller used his Four-Seam up in the zone to righties which is where he got most of his whiffs with the pitch. He used the Slider to work down and away from the righties with an occasional front door breaker also getting mixed in. He threw his Cutter up-and-in to righties primarily when he was ahead in the count, and threw it down and away the rest of the time. I think this was to play off the similar look of the Slider and Cutter out of his hand as well as both pitches breaking gloveside. This allowed him to get hitters to miss-time the pitch if they were looking for a Slider out of the hand. He only threw the Changeup 3 times to righties so there isn’t much to analyze there. To lefties, Miller dropped his Four-Seam usage to 50%, and swapped the Cutter and Slider, using them at 25% and 15% respectively. He also threw a Changeup 10% of the time. Miller used the Cutter heavily on the inside part of the plate to lefties and kept the Slider on the outer portion. He also left the zone quite a bit with the Slider to get some chases when he was ahead in the count. His strategy was the same with the Four-Seam as it was to righties, staying primarily up in the strike zone.


In 2024, Miller went from being a starter to being a closer for the A’s, so he scrapped his Cutter and Changeup to begin using a Four-Seam and Slider mix. Miller has thrown his Four-Seam to lefties 71% of the time so far, and his Slider 29%. He favors the Slider over the Four-Seam to righties, throwing it 55% vs. 45% for the Four-Seam. The interesting thing I noticed is that he seems to throw 2 different Sliders, one to righties and one to lefties. His Slider to lefties has much less glove-side break than the Slider he throws to righties, and therefore drops a lot more because of that. So maybe Miller didn’t completely get rid of his Cutter, but instead killed some vertical movement to vary it more from his Four-Seam so that he basically has a 3rd pitch he can use to lefties exclusively. Miller didn’t throw his Changeup much in 2023, but when he did throw it he threw it to lefties. His Changeup wasn’t a terrible pitch for him, and he got a 42.9% whiff rate with it which is almost double the league average. The reason he dropped the pitch is likely because he lacked the necessary control of it to make it useful, as he also only threw the Changeup in the zone 23.3% of the time in 2023. Some of this is by design to generate chase, but he only did this with 13% of the Changeups he threw, so in the end those pitches out of the zone weren’t productive.


Now let’s go over Miller’s production and see if the changes he made have paid off for him and the A’s. In 2023, Miller generated an above-average amount of fly balls and line drives, but struggled to find success with the Cutter, which produced an xwOBA of .379 against it. I hate to blame the failure of his Cutter on its lack of movement entirely, as many pitchers have found success with gyro sliders which have no movement at all, but his Cutter fell right between his Slider and Four-Seam on his movement plot, meaning it didn’t differ enough from the 2 in my opinion, and it didn’t have enough glove-side break to give lefties trouble on the inner part of the plate. His Four-Seam also got hit hard often, with a .298 xwOBA against it on the year. I believe this is because of the issue I mentioned before with his Cutter shape not differing enough, but it also could be because of the counts he was throwing the Four-Seam in. Miller favored the Four-Seam in every count except for 0-2 last season, and even in 0-2 counts he still threw it 35% of the time. I think he relied on the Four-Seam too much, especially in counts where he was ahead when he didn’t need to give the batter a great pitch to hit. These counts are where I think it would’ve been good to fit in more Changeups which he really didn’t show much as I said before. His Slider performed pretty well last season, with a .207 xwOBA against it and a 47.1% whiff rate. His Changeup, while not used much, had a 92.6 mph average exit velocity on it.


This season, however, the script has completely flipped for Miller, whose Four-Seam is being whiffed on at a 47.4% rate and only has a .197 xwOBA against it. Miller’s Slider has also gotten even better, with a 46.9% whiff rate and a minuscule .076 xwOBA against it. I think the main factor in Miller’s improved performance is being moved into the closer role for the A’s. Miller is now able to do what he is best at over the course of just a few batters, which is keeping the Four-Seam at the top of the zone and the Slider breaking away from righties at the bottom of the zone or falling out of the zone to lefties. As a starter, Miller was forced to add pitches to his arsenal that he either couldn’t command or that weren’t effective for him such as the Cutter and Changeup, but now, as a closer, he doesn’t have to worry about going through a lineup multiple times and having to figure out different ways to get guys out, because his 2 pitches are elite and they are all he needs. It has also helped to add 2 mph to all of Miller’s pitches because he now doesn’t have to worry about eating innings, and instead can just empty the tank.


Mason Miller's transformation from a struggling rookie starter to a dominant closer is a testament to his adaptability. By honing his craft with pitch design, and optimizing his productivity by playing to his strengths, Miller has become a formidable force on the mound. As he continues to deliver outstanding performances, Miller's journey serves as an inspiring underdog story, highlighting that success is sometimes hiding in plain sight. As the trade deadline approaches, his meteoric rise and impact on the A's season will undoubtedly make him a sought-after asset.


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