One ugly stat sums up why the Red Sox will regret the Aroldis Chapman signing

In 2024, the Boston Red Sox struggled with a torrent of pitching problems which likely cost them a Wild Card spot. The team tried to address its bullpen issues at the trade deadline, but those were only temporary fixes, as their flurry of acquisitions are now back on the free agent market. Kenley Jansen is finally out the door, as are Chris Martin, Luis Garcia, Lucas Sims, Rich Hill and Brad Keller who has signed with the Chiba Lotte Marines of the KBO.

So while names Juan Soto and Max Fried drew all the attention, rebuilding Boston's bullpen was also high on Craig Breslow's to-do list. And this week, he turned to a former rival, Aroldis Chapman, to do just that, and compensated him very generously in the process.

The sweaty flamethrower has long been known for throwing overpowering fastballs at over 100 mph. And though he has aged since his prime, he can still ramp it up when need be. However, his performance last season was anything but elite: Chapman posted a 3.79 ERA with 98 strikeouts through 61.2 innings, missing plenty of bats but also missing the strike zone almost as often. The Red Sox are no doubt hoping they can tap into that upside, but they might have some unexpected trouble with getting Chapman to settle down in his new home ballpark.

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Aroldis Chapman’s ERA at Fenway Park is unsightly

When it comes to pitching in Boston, Chapman appears to struggle mightily. His career ERA at Fenway stands at a miserable 5.71 through 17.1 innings. This is worse than at any other ballpark where he has thrown at minimum of 14 innings, and it's his sixth-worst mark overall (his ERA in Houston stands at 6.08 through 13.1 innings, the only other ballpark where he has pitched more than eight innings and maintains a higher ERA than at Fenway). Could this just be a Red Sox thing? Is it possible all of these struggles just indicate he had a hard time pitching to the once-formidable Boston batting order?

In his career, Chapman has thrown 44.2 innings against the Red Sox. Over that span, he maintains a much more respectable 4.23 ERA. In fact, his ERA at Fenway is worse than when facing every other MLB team but one: In 22.1 career innings against the Mets, he posted a 6.85 ERA. Against the other 29 teams, his various opponent ERAs are lower than at Fenway (5.40 and lower).

All things considered, the Red Sox may have been one of, if not the, worst fits for Chapman. He has proven he can still hurl and maybe his 17.1 innings are a sample size he can easily outgrow, but as the 2025 season begins, it may be worth it to keep a close eye on his home and away splits.