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Aroldis Chapman’s fastballs have started drifting over the middle of the plate again — and that could be a problem

Aroldis Chapman has, unfortunately, had an incredible comeback season in 2025, I’ll admit it. Even as someone who never has — and never will — want him on my team, his dominance in the ninth this year has truly been a sight to behold. While it’s morally reprehensible to truly be a “fan” of his at this point in his tumultuous MLB journey, his success has certainly been conducive to Boston’s playoff-hopeful performance thus far in 2025.

But as his astounding 50-batter hitless streak came to an end in Sacramento last week, his fantastic season — which has been due to many factors, including the luck that exists in every event in baseball — seemed to regress to the “known” version of Aroldis Chapman.

There is no question that he’s had a fantastic year for any closer out there, but even more so as a 36-year-old thought to be a few years on the decline. And while this change is due to a few improving factors (most notably his fastball location), some of it, as will almost always be the case, is due to luck. When I say luck in this situation, I mean luck in the least drastic sense of the word possible. I mean that he has been a very good pitcher, luck or no luck, but his numbers have been helped by a bit of luck.

The ERA luck is minimal when you keep in mind how good his stat line still would be if he pitched to his 1.70 FIP as opposed to his 1.26 ERA, but that’s still more variant than you’d expect to see. All of this is to say that he has, without a doubt, been a great closer this year, but has taken some of the bad luck he experienced last season and turned it into a positive this year.

He actually should have been pretty good in 2024, and wasn’t necessarily bad, outside of his first percentile walk rate. But playing in front of the Pirates (and having less concentrated fastball location) resulted in a nearly 0.80 difference between his ERA and xERA. I guess what I’m saying is what goes around comes around, as is common in larger sample sizes in general, but not always observed in practice in baseball.

And as both luck and age catch up with the veteran, his past few outings have shown some mild causes for concern, not only due to the velocity dip he’s seen in September (which has been widely discussed), but more importantly because of his faltering command as it relates to this season’s location improvements. I’m much less concerned when it comes to his velocity, considering he’s 36 and has appeared in 62 games thus far this year. But his leaks in fastball command, especially as he’s had to rely more on his breaking pitches due to the velocity drop, are more of a cause for concern as Boston heads into its most crucial stretch of the season.

This concern is multiplied by the fact that Justin Slaten has not at all looked like the back-end bullpen guy we’d come to know since his return from the IL, leaving the Red Sox without a true closer replacement should things take a turn for the worse.

Here’s a look at Chapman’s pitches thrown in the zone against the Athletics and Yankees in two of his most recent outings:

While the maps don’t point to a glaring problem on their own, it’s clear that Chapman’s had fastballs leaking over the middle much more often in September than he has had for the rest of the year. This itself isn’t an inherent problem (as seen by the location chart below, when Chapman threw a good amount of fastballs deeper in the zone but allowed contact on none of them), but the contact being made on these balls left over the plate is.

In his appearance against the Athletics, in which his dominant streak came to an end, batters made contact with five of the seven fastballs he threw, which included Lawrence Butler’s walk-off single in the ninth. Against the Yankees a few days later, he once again gave up a run and a pair of hits, as batters made contact on six of ten fastballs, including Cody Bellinger’s RBI double to pretty much clinch the game for New York.

We’ve heard all year about how Connor Wong got Chapman to take another look at how and where he locates his flamethrower fastball this year, so it’s even more interesting that these past few blips on Chapman’s season have come with Wong behind the plate.

It’s standard knowledge that a fastball leaking over the plate is never a good thing in baseball, and even though these instances have been few, the fact that they’re showing up in a much more concentrated manner than before during a critical part of the year, as Boston hopes to still make it into the playoffs, is worrisome. Let’s face it: Chapman is old. And even though he’s had success for the majority of the year, that’s unlikely to continue if the combination of his slight dip in velocity and struggling control persists. Red Sox fans know all too well just what he can turn into when that wild fastball loses control, whether that means an uptick in walks or hard contact.

Another layer of concern comes to light when considering that Chapman’s success with fastball location has largely been a new thing this year, meaning he has nearly 15 seasons of experience not operating this way, which is a lot easier to mechanically, or mentally, revert to than a process you’ve been using for 62 games out of your 858 career appearances.