Aroldis Chapman looks as dominant as ever, even entering his age-38 season in 2026. But when the Red Sox signed him last winter, he was a little bit of a gamble.
When he joined the Sox, Chapman was coming off a rocky season (for him, at least) and getting into his late 30s. But in Boston, he wasted no time re-establishing himself as an unstoppable force on the mound, and his debut season with the Red Sox ended in American League Reliever of the Year honors.
Here are the two big reasons why vintage Chapman came back this year.
1) He got his stuff under control
Chapman's stuff is so electric that, at times, he can also be erratic. Those 100 mph lefty fastballs and sharp-breaking sliders get away from him.
That's when he struggles, and it was a growing problem in the last few years. Chapman was still striking out tons of guys, but he was also walking tons of guys, and his wild command was causing some poor numbers by his standards.
It peaked in 2024. Command was by far Chapman's biggest problem.
Chapman's walk rate spiked to over 14% -- in the bottom 1% of MLB pitchers. If there's one thing that can even partially neutralize Chapman's stuff, it's the inability to locate it. Chapman missing badly with his pitches allowed hitters to hit him harder when he finally did get into the zone.
The issue was particularly bad with his fastball and slider. Chapman's walk rate in plate appearances ending on his four-seamer was a sky-high 29%. His walk rate in plate appearances ending on his slider was 19%. That's bad.
But in 2025, he found his command. Chapman fixed pretty much every problem he had. And when Chapman is locating his pitches, he's extremely scary. His stuff is still just too good to hit.
Chapman's walk rate improvements, 2024 vs. 2025
- Overall: 14% to 7%
- PA ending on 4-seamers: 29% to 11%
- PA ending on sliders: 19% to 3%
Chapman got ahead of hitters way more often in Boston than the year before with the Pirates. In 2025, he was ahead in the count a career-best 40% of the time -- up from just 31% of the time in 2024.
He rarely even put himself at risk of walking hitters, going to three-ball counts on a career-low 14% of plate appearances -- down from 27% of plate appearances in 2024.
And when he did go to three balls, he found the strike zone. Chapman had an in-zone rate of 62% in three-ball counts in 2025, the second-highest mark of his career and his highest since 2016. In 2024, only 54% of the pitches he threw with three balls landed in the zone.
He was particularly better at locating his previously problematic pitches, the four-seamer and slider, in those risky three-ball situations. He kept those pitches in the zone a career-high 69% of the time in three-ball counts -- up from just 54% of the time in 2024.
Chapman's vast improvements in command produced a vintage Chapman season, because he's still so nasty that he strikes out as many hitters as ever. He just got rid of the thing that was hurting him the most while keeping all the good stuff.
2) His 4-seamer doesn't have to do all the work anymore
For the first half of his career, Chapman was, for all intents and purposes, a one-pitch pitcher. His 100 mph heater was all he needed.
Then his four-seamer got a tiny bit less unhittable (emphasis on a tiny bit), and he got a little more erratic, and even he had to change. The key to that change was a second type of fastball in his repertoire. And his 2025 season with the Red Sox is proof he changed successfully.
From 2010 through 2017, his first eight seasons in the Major Leagues, Chapman threw his four-seam fastball 80% of the time. You can do that when you have the most dominant fastball of your generation. Chapman would mix in sliders every once in a while, but those were really just for show.
Of course, no fastball lasts forever -- not at its max velocity, at least -- and as Chapman got into his 30s, even he lost a tiny bit of juice. His fastball still hits triple digits and beyond with alarming regularity (for opposing hitters, that is), just not quite at its apex levels of the past.
But by now, Chapman has evolved. It was slow going at first, but Chapman has discovered a more balanced pitch mix that takes some pressure off the four-seamer that used to carry almost all of the load.
One part of that is the slider he's already thrown. A bigger part is the nasty low-90s splitter he started throwing in 2020. But the biggest part of all is Chapman's sinker.
Entering 2026, Chapman now throws nearly as many sinkers as he does four-seamers. He's followed the trend of the Major Leagues, where pitchers increasingly throw more than one type of fastball to show hitters different looks. Even the pitchers with the most electric stuff are doing it, and that includes Chapman.
The 2025 season was the highest sinker usage of Chapman's career. He threw 34% sinkers, to go along with his 40% four-seamers, 15% sliders and 11% splitters.
Most crucially, Chapman's two types of fastball last season allowed him to control both sides of the plate against both righties and lefties. With the Red Sox, he pounded right-handed hitters up and in with four-seamers and peppered them up and away with sinkers. Against left-handed hitters, he did the opposite, firing four-seamers past them up and away and running sinkers up and in on their hands.
Having two different heaters, that he can throw in triple digits to opposite sides of the zone, made Chapman unfair again in Boston in 2025.
His four-seamer is still elite, and it can still do a lot on its own, but it doesn't have to do everything. His sinker tends to be even a little faster than his four-seamer, and it blows hitters away just as well. After all these years, his four-seamer can finally take a breather. The Red Sox are reaping the rewards.