It’s been a hot start to the 2024 season for the Boston Red Sox. They started the season with a 10-game road trip to the West Coast and arrived home Monday at 7-3 after a four-game split in Seattle, a three-game sweep in what will likely be their final trip to play the A’s in Oakland, and a 2-1 series win over the Angels. While Boston hasn’t exactly met the highest of competition yet — this week’s home-opening series with Baltimore should be a serious test — the Sox entered Tuesday with the second-best run differential in the majors, at +26. Aside from the Trevor Story’s injury, which as Jon Becker explained yesterday is going to test Boston’s uninspiring middle infield depth, it’s been an encouraging first two weeks for Alex Cora’s club.

Somewhat unexpectedly, pitching has been the story of Boston’s early success, after the Red Sox redesigned their pitching infrastructure over the offseason. In this regard, two of the most important additions to the club are not current players but former big league pitchers: Craig Breslow, who replaced Chaim Bloom as the team’s chief baseball officer, and Andrew Bailey, the new pitching coach. After pitching as a reliever for 12 years in the majors, including parts of five seasons with the Red Sox, Breslow spent five years in the Cubs’ front office working to overhaul their pitching program. One of Breslow’s first moves was to hire Bailey, his former Red Sox teammate. Bailey, a two-time All-Star and the 2009 American League Rookie of the Year, came over from the Giants, where he held the same role and helped to develop the likes of Logan Webb, Kevin Gausman, and Carlos Rodón into some of baseball’s top pitchers recent years. Boston also hired Justin Willard to a role it titled “director of pitching.”

Entering Tuesday, Red Sox pitchers lead the majors with a 1.49 ERA, a 2.92 FIP, a 3.08 xFIP, 10.49 strikeouts per nine, and 2.4 WAR. Two times through the rotation, Tanner Houck hasn’t allowed a run, and Nick Pivetta, Kutter Crawford, and Garrett Whitlock have allowed one earned run each. The bullpen has supported this rotation capably, too — in 37.1 innings, Boston relievers rank second in baseball with 0.8 WAR, third with a 1.45 ERA and 3.40 xFIP, and fourth with a 3.18 FIP. All of this from a staff that features mostly the same members from a group that struggled last season. It’s too early to know for sure if 2024 will be any different, but this is an auspicious start.

With new leadership in place, the pitching approach from the Red Sox has looked remarkably different so far. Most notably, they’re throwing far fewer fastballs and mostly abandoning the four-seamer. After throwing four-seamers 26.1% of the time in 2023, they’re down to a league-low 12.9% in 2024, compared to the league average of 31.3%. (San Francisco, Bailey’s former team, throws the second-fewest percentage of four-seamers, at 18.8%.) Pivetta, who threw four-seamers around 50% of the time for the first seven years of his career, is down to 32.8% and instead is ramping up the usage of his cutter and sweeper. Brayan Bello, who at 24 is the youngest member of the rotation and who signed a six-year extension in March, has eliminated a four-seamer he used 20.6% of the time last year. So has Houck, who threw it 9.9% of the time last year — and 38.6% of the time as recently as 2021. They’ve both ditched it for sinkers. Key bullpen arm Chris Martin threw exactly the same number of cutters and four-seamers last year (249), for a usage of 34.5% each; so far this year, 56.6% of his pitches are cutters, compared to just 13.3% four-seamers.

The message from Bailey and his staff might be that four-seamers aren’t all that. In a great piece from The Athletic’s Jen McCaffrey last week, Bailey talked about how vulnerable fastballs can be to serious damage, and none more so than four-seamers. In 2023, the pitch was hit hard across baseball, with the league posting a .349 wOBA and .352 xwOBA on over 230,000 pitches. Sinkers weren’t much better, with opposing hitters recording a .345 wOBA and .353 xwOBA against them. Cutters outperformed both, yielding a .337 wOBA and .338 xwOBA against.

The difference was more pronounced, though, when looking at heaters thrown no harder than 95 mph. In those cases, four-seamers were hit to a .371 wOBA and .372 xwOBA, sinkers to a .355 wOBA and .363 xwOBA, and cutters to a .339 wOBA and .341 xwOBA. At these lower speeds, fastballs without much movement likely were not hard enough to overwhelm batters; as Bailey sees it, adding some cut or sink might help these relatively slower-throwing pitchers. The data appears to back that up:

It could have been the case for Bello and Houck, in particular, whose four-seamers have graded as below average on the Stuff+ scale. Bello threw his at 95.5 mph on average, last year, but it left a lot to be desired; hitters posted a .424 wOBA off the pitch, while his sinker and changeup far outperformed it. Houck threw his at 93.9 mph and with less-than-average movement in both dimensions, and hitters handled that to the tune of a .425 wOBA.

Pivetta is a more nuanced case. His four-seamer has played nicely, the stuff metrics like it, and it’s a little more distinct than his other offerings — he throws it at 94 mph, and nothing else over 90. He’s still using it as his primary pitch, but mixing in more cutters and more of his three breaking balls, most prominently the sweeper that he introduced last year. As for the other Sox starters, Crawford is using his primary four-seamer (which might be the best in the rotation) just a bit less, but has also cranked up the usage of his sweeper to nearly the same level — around a third of his pitches. Whitlock retired a seldom-used four-seamer last year; he has introduced a cutter alongside his go-to sinker, but he’s dialed back fastball usage altogether in favor of more changeups, sweepers, and sliders.

In general, the team is working to be less reliant on all fastballs. Some of this is specific game-planning — the Mariners and Angels, two of Boston’s first opponents, were in the top third of the league against fastballs in 2023 (though the Angels’ 2024 lineup is short one particular elite fastball hitter). But Bailey spoke to the press about the importance of soft offspeed and breaking pitches on limiting hard contact, and the Red Sox seem committed to that plan. Last year, they ranked second in baseball with a 61.3% overall fastball usage. (Bailey’s Giants were dead last at 44.4%.) In 2024, Boston is down to 51.7%, which ranks 22nd. All five starters are throwing fastballs at lower rates than they did last year, with Bello, Whitlock, and Houck falling below 50%. The team went from 24th in breaking ball usage (28.4%) last year to sixth (34.6%) in the early goings this season. In five relief outings, newcomer Isaiah Campbell has thrown 40 sliders, 20 sweepers, and just five fastballs.

For Bailey and Boston’s run prevention unit, it seems to be about breaking the habit of going back to a fastball just because it seems like some sort of default. Here’s a look at last year’s pitch breakdown, led by four-seamers, sinkers, sliders, and cutters:

And here is this year’s, with sinkers, sliders, and sweepers all outnumbering four-seamers:

How is using soft offspeed and breaking pitches to limit hard contact going for the Red Sox? Well, no team has a lower average exit velocity than their 86.7 mph. Opposing hitters have a .199 wOBA against their breaking pitches — the lowest mark in baseball — and a .228 xwOBA, which is the second lowest; their breaking pitches have been worth 1.8 runs per 100 pitches, the highest breaking-ball run value in the majors. Their offspeed stuff hasn’t fared as well, with a .253 wOBA against that’s 12th-best in the majors and a .310 xwOBA against (17th), but they’ll live with that, considering the increase in offspeed pitches and breaking balls seems to have made their fastballs more effective, too; they’re allowing a .270 wOBA against heaters, which ranks second best in the sport, and a league-low .301 xwOBA.

Bailey and Co. aren’t alone in their skepticism of fastballs, and particularly four-seamers. Leaguewide four-seamer usage has been trending downward since 2021, falling from 35.4% that year to 32.2% in 2023 and 31.3% so far this year. But the Red Sox seem to be asking: Why even throw that many? If we’re starting to lose faith in four-seamers — particularly the unspectacular ones — why use a third of our pitches on them? Why not get ahead of the curve — or, more precisely, ahead of the fastball — in terms of cutting out the heat?

The caveats of April are serious — the Red Sox haven’t even thrown a pitch at Fenway Park yet. But what might be most exciting for Boston fans is the establishment of a pitching infrastructure that seems to have some conviction in the direction it’s headed, with buy-in from the players to the front office. For a franchise that has struggled mightily to develop young pitching talent for a while now, that’s a big step in the right direction.

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