There’s a reason that the trade deadline sees a large number of relief arms being shipped around the country. Baseball teams crave stability for those high-leverage, end of game situations in August and September. In October, it’s critical that your bullpen be performing better than everyone else’s because if not, you are at a severe disadvantage when it matters most.
Knowing this, the Boston Red Sox took a chance on lefty Aroldis Chapman. “Took a chance” is probably not the right phrase, but they banked on Chapman to provide a lot of value for their bullpen by giving him $10 million for the year. Chapman’s been the subject of a domestic violence issue in the past, and has had some shaky seasons here and there. What he hasn’t had is a loss in his stuff. If you aren’t aware, Chapman originally gained fame in baseball because of his elite fastball and he owns 4 of the 5 hardest thrown pitches ever, including the fastest at 105.8 mph. He’s still slinging that fastball now 15 years later, hitting 103.8mph this season!
At 365 career saves, Chapman sits 13th ever, and he’s just 25 saves from the 9th place man (Dennis Eckersley, 390 saves). “The Cuban Missile” is a legend, but he’s no where near finished.
There are underlying metrics to look at when assessing the exceptional 2025 season that has earned Chapman another $13M for next season to stay in Boston, and we’re going to walk through them now.
Chapman’s 2025
57.1 IP, 1.26 ERA, 1.70 FIP, 38.7 K%, 6.6 BB%, 0.47 HR/9, 0.68 WHIP, .195 BABIP
Pretty insane. He’s been hitting on all cylinders, and it’s important to understand how he’s evolved as a pitcher throughout his career to truly appreciate it.
Coming up in the pros, Chapman was known for his heater. He leaned heavily on the pitch. For example, in 2012, he threw 1,054 four seam fastballs (87.%) compared to just 145 sliders (12.1%). This wasn’t an issue because it was just an unhittable pitch. That 2012 season was his best season statistically until 2025.
It wasn’t until the last 5-7 years that Chapman began introducing pitches to his arsenal. He didn’t do that because he was losing velocity; he did it to evolve as a pitcher and further deceive hitters. This season, 2025, his four seam usage is at 39%, sinker 34% and both his slider and split finger change 14%. Take a look at how his pitch usage has changed over the years (from Baseball Savant):
He’s become more unpredictable than ever. With a fastball that still makes a hitter’s knees shake, Chapman has them on their heels at all times, and there’s not much the hitter can do on a pitch with spin. Baseball Savant still has Chapman in the 97th percentile in fastball velocity and fastball run value. Not all his fastballs are the same, either. His 4-seam rides up and toward Chapman’s glove side, so moving inside against lefties and away from righties. His sinker complements his fearsome 4-seam with added movement, and he loves to throw it with 2 strikes to fool his opponent.
Chapman’s sinker, according to Statcast, has given up a 0.95 AVG, a .189 SLG, and a .140 wOBA. That’s silly. That pitch also has the highest whiff rate of all sinkers (37.4%). Don’t forget about the slider too. That pitch has given up a .161 AVG, .161 SLG, and .163 wOBA. When hitters swing at his slider, they miss 47.9% of the time! Finally, I won’t list the numbers for his split-finger changeup because I’d sound like a broken record.
So what we can deduce from this analysis is that the stuff is there. In fact, he may have the best stuff he’s ever had in his career, which is fun to think about. But there’s more to Chapman’s 2025 than this.
He’s always been one of, if not the best strikeout pitcher in baseball. As a closer, he holds nothing back. (According to Baseball-Reference’s Stathead, Chapman ranks 12th among all relievers ever in strikeouts with 1328, and for the record, he’s seen thousands of batter less than the other guys on the list. Crazy.) FanGraphs tells us he has a career strikeout rate of 39.9%, and this year, as you saw above, he’s right around there. But this year is different because Chapman’s 6.6% walk rate in 2025 is basically half of his career 12.2% walk rate.
How’s he doing it? Well, to put it simply, he clearly feels good. But on a more strategic level, he’s throwing first-pitch strikes 70.8% of the time, according to Statcast. That’s well above his career rate of 58.1%. As a flamethrower (this applies to any pitcher, really), to get ahead in the count is a major advantage. Hitters are swinging freely more than ever as it is, so to dig them even deeper gives Chapman a chokehold on them.
Baseball-Reference further shows just how impossible it’s been to do anything productive against Chapman when he’s got 2 strikes on you. First off, with 2 strikes, his strikeout-to-walk ratio is 11.71. Holy moly. Now, he’s gotten himself into just 19 3-2 counts this season, resulting in 7 walks, but the fact he’s been in 139 total two-strike counts shows how efficient Chapman’s been at throwing strikes. In two-strike counts, he’s given up a .069 AVG, .115 OBP and .092 SLG. Essentially… good luck guys! Perhaps Chapman has found out how to aim small, miss small, how to just be more aggressive because he realized his stuff is that good, or mechanically altered his motion as to hit the spots he’s always aimed for. Regardless, he’s figured it out.
His value has skyrocketed because it signals that not only is his stuff great, his command might even be greater. His reliability grows to new levels.
Historical Context
Among Red Sox Relievers:
To this point, Chapman’s year ranks with the greatest Red Sox reliever seasons of all time. Among Red Sox reliever seasons of at least 50.0 IP, Chapman ranks 4th in ERA (1.26), 4th in ERA+ (332), 4th in FIP (1.70), and 2nd in WHIP (0.68).
Among Lefty Relievers:
Teams these days will pay a lot for premium lefty arms. In baseball history, plenty of left-handed relievers have put together special seasons, but Chapman’s 2025 ranks 10th in ERA and ERA+, 8th in FIP, and 1st in WHIP. By the way, Chapman’s 2014, 2016 and 2012 seasons rank 1st, 2nd and 4th in FIP among left handed relievers with a minimum 50.0 IP.
Finally, no lefty reliever aged 37 or older has put together a season like this. Chapman’s ERA, ERA+, FIP, WHIP, H/9, and K-to-BB ratio all rank number 1.
Takeaways
If you are capable, take in high leverage innings of Red Sox games as we enter late September and October. Aroldis Chapman is simply must-watch baseball and impossible to disappoint. I will be curious to see how he attacks the last couple weeks and, barring a collapse of all collapses, the playoffs. It takes a team to win in the postseason, especially in baseball, but the Red Sox can at least rely on one 6’4″ behemoth of a southpaw to shut down a hitter or three when called upon.
Inner Half 