Article: Garrett Whitlock the Reliever is So Much Better Than Garrett Whitlock the Starter

[Brandon Glick]

To no one's surprise, Aroldis Chapman leads the Red Sox's bullpen in most notable categories this season, including fWAR (1.8). The man directly behind him on that list, Garrett Whitlock, is also the longest-tenured member of the relief crew, having been acquired via the Rule 5 Draft from the New York Yankees in 2020. In fact, the only reliever on the 40-man roster who has been in Boston longer than Whitlock is Chris Murphy, who is just one of two relievers with a 40-man spot that was actually drafted by the organization (the other being Luis Guerrero).

While that organizational philosophy on how to build a bullpen warrants its own deep-dive in the future—it's emblematic of the way the Cubs, Craig Breslow's old stomping grounds, continue to turn their bullpen over on a yearly basis—Whitlock is the one who will be cast into the spotlight today. The 29-year-old right-hander is the owner of a tidy 2.77 ERA and even more impressive 2.48 FIP through 55 1/3 innings this season, hence his 1.4 fWAR. Whitlock's 46 appearances ties his career high that he set in his rookie campaign back in 2021, the only other season of his career in which he's exclusively been a reliever.

That last point is important, because it's clear that Whitlock is better in a bullpen role. He's started 23 games in his career, all coming between 2022-24, and he's been relatively solid in those games: 109.0 innings, 4.29 ERA, 1.27 WHIP, 102 strikeouts against 23 walks, and a .217/.313/.450 batting line allowed. Those are the numbers of a passable No. 5 starter, though averaging just 4.8 innings per start hardly qualifies Whitlock the starter as anything more.

Now, turn your attention to his stats as a reliever: 188.0 innings, 2.68 ERA, 1.07 WHIP, 218 strikeouts against 50 walks, and a .217/.275/.335 batting line allowed. Those are the numbers of a really good set-up man, and it's worth considering that the OPS+ of opposing hitters falls by more than 40 points when Whitlock comes out of the bullpen as opposed to starting the game on the mound. He's also allowed the same number of home runs (16) in nearly 80 more innings as a reliever.

The first place your mind should go when hearing that a pitcher is having more success in the bullpen is velocity, and that instinct is very much correct. In 2021, Whitlock's sinker averaged 95.9 mph. That velocity dropped a tick in 2022, and in 2023-24, his sinker averaged less than 94 mph. He did make most of his appearances out of the bullpen in those years, but it's clear that a starter's workload (and some injuries) limited the capacity of his arm. Back to his full-time relief duties in 2025, Whitlock's sinker is once again at its fastest point, averaging nearly 96 mph.

That's certainly a big reason why Whitlock has been more effective as a reliever, but it's not the only one. In fact, he's made some noticeable changes in 2025 that point to systematic changes in his approach on the mound. I won't toss five scatter plots in your face right now, but take a look at Whitlock's movement profile from 2021 to 2023 to 2025 (courtesy of Baseball Savant).

That's a pretty drastic difference, created mostly by turning his sinker into a faux four-seamer (more riser and less run) and getting some much-needed drop on his changeup. The numbers don't lie: in 2023, Whitlock's sinker averaged 12.8 inches of rise and 15.4 inches of run. Those numbers in 2025 are at 14.9 inches of rise and 13.2 inches of run. That's a sizable difference in both directions, and it's turned his sinker into a genuine primary fastball again, allowing him to ditch the four-seamer that rarely, if ever, was worthwhile to throw.

It also helps that he's finally settled on throwing both a sweeper and a slider after years of trading one off for the other; the sweeper, on average, gets nearly seven more inches of break than his slider, which in turn functions like a "power breaker" thanks to its tighter break and faster velocity. These aren't revolutionary changes, but creating a distinction in his movement profile has allowed Whitlock to be more purposeful with his pitches. No longer are there offerings tossed in there to simply throw the hitter off balance—every pitch is thrown with intention.

So, what's the takeaway here? Well, Whitlock's case is a reminder that some guys are simply just better coming out of the bullpen; pitching short spurts is often an easier task than having to reserve bullets for the third time through an order, and allows for a pitcher to condense their arsenal to their best pitches, rather than having to reach for subpar offerings. It's also a self-evident truth that diversification in a pitch mix is extremely important, and it's a testament to both the Red Sox and Whitlock that they've been able to hone in on the spin and movement of his pitches in order to tailor the perfect combination.

None of this is to say what Whitlock has done is easily repeatable—quite the opposite. It's hard work for a pitcher who is around the MLB average as a starter (which is still one of the best players in the world!) to try something different and accept a "demotion" in their role to the bullpen. Credit to him for making the most of this situation, and turning into one of the most valuable members of the Red Sox's pitching staff.

 

View full article

[moonslav59]

If only Bloom understood facts.

[Kimmi]

I have no problem with the Red Sox trying out Whitlock as a starter.  A solid starter has more value than a solid reliever.  It didn't work out, but it was worth the try.  That said, I'm glad that he is once again a key piece of our bullpen.