BOSTON — Prior to last season, the Boston Red Sox renovated the home clubhouse, constructing new maple lockers, adding 16 TV displays and updating the lighting and sound systems to create a modern, sleek look. Maybe most importantly, there is also room to squeeze in a couple of temporary lockers — no small consideration given the current state of the team.

The Red Sox have 13 players on the injured list. It’s been a carousel of players coming and going to fill those spots, lockers emptied for those designated for assignment or sent down to the minors, new ones squeezed into the middle of the floor.

“It’s crazy. Definitely more than I can remember,” outfielder Tyler O’Neill said. “Obviously, we have a lot of star players on the list right now. That sucks. It’s up to the rest of us guys to take a step up to try and fill those holes, but man, we want those guys on the field for sure.”

In April, the Red Sox lost more days and more player dollars to the IL than any other team. Four-fifths of their projected starting rotation is injured, with Lucas Giolito out for the season. Shortstop Trevor Story is also out for the season after fracturing his shoulder. Cleanup hitter Triston Casas, who posted an OPS over 1.000 in the second half in 2023, is out two months with torn cartilage in his rib cage. Designated hitter Masataka Yoshida landed on the IL last week with a hand injury. O’Neill even missed a week himself after suffering a concussion in a collision with third baseman Rafael Devers.

Craig Breslow, the first-year chief baseball officer, has been busy just trying to keep the 26-man active roster filled, while manager Alex Cora has had no choice but to be pragmatic about the whole situation, as the team makes moves on the fly to shore up the roster before a game. Cora believes bench production can help a team win eight or nine games a season — and the Red Sox are certainly testing the limits of that theory right now.

“It’s a star-driven league, we know that, but what you do with the edge of the roster is very important,” Cora said. “We work so hard on chemistry and culture in spring training. Then you have a whole different team in the beginning of May. It’s going to keep changing, but I do believe we’re in a good place. We’re playing good baseball, which is awesome.”

Indeed, the Red Sox beat the Minnesota Twins 9-2 on Sunday to snap a three-game skid and end Minnesota’s 12-game winning streak. Boston is 19-16, within shouting distance of the Baltimore Orioles and New York Yankees in the American League East despite all the injuries.

How have the Red Sox done it? The pitching staff is atop the majors with a 2.59 ERA led by a rotation that has posted the lowest ERA (2.10) through a team’s first 35 games since the 1981 Dodgers had a 2.06 mark. With Giolito (Tommy John surgery), Brayan Bello (back tightness), Nick Pivetta (elbow strain) and Garrett Whitlock (oblique strain) all sidelined at the moment (although Pivetta is expected to return this week), Tanner Houck and Kutter Crawford have stepped up to lead the group — but the success can be attributed as much to a change in philosophy as any one starter’s improvement.

“If we keep doing the things we’re doing on the mound, it doesn’t matter who comes in,” Cora said. “We’re going to be in a good place.”

Breslow and Red Sox pitching coach Andrew Bailey insist their approach to pitching, while unprecedented, isn’t some kind of revolution.

The two were bullpen teammates with the Oakland Athletics and Red Sox during their playing days. They remained friends as Breslow worked for the Chicago Cubs from 2019 to 2023, first as director of pitching and then as assistant GM/vice president of pitching, while Bailey worked as a coach with the Los Angeles Angels and then as the San Francisco Giants’ pitching coach the past four seasons.

“We talked a lot about staying in the game of baseball and working together. Craig’s a brilliant mind and you always knew he was going to be a GM or a manager,” Bailey said, not even mentioning the fact that Breslow majored in molecular biophysics and biochemistry at Yale. “So, yeah, I was like, ‘If you never need a bullpen coach or a pitching coach.'”

After the Red Sox hired Breslow in late October, one of his first calls was to Bailey. Since joining Boston, Bailey has implemented a concept that was one of the trademarks of the Giants under his guidance and has been the key to Boston’s pitching success this season: fewer fastballs.

The Red Sox are throwing the fewest fastballs of any team in MLB in 2024. Just 31.8% of their pitches have been fastballs (either four-seamers or sinkers), well below the MLB average of 47%. Just one other team is under 40%, and no team was below that last season.

“I know a lot has been made of this,” Breslow said, “but if you were to take a step back and say, ‘OK, we can rank all of your pitches and what we’re asking you to do is take your best pitch and throw it more and take your worst pitches and throw them less,’ I don’t think anyone would be like, ‘You’ve reinvented the game.’

“I think what we have done is refuse to be beholden to traditional baseball thought, which says you have to be able to throw a fastball down and away. I would argue you have to be able to throw a pitch over the plate. I have no idea why that has to be a fastball.”

What the Red Sox are doing is simply a more extreme version of a trend we’ve seen across the sport. Detailed pitch tracking data goes back to 2008, and the percentage of fastballs has steadily dropped since then:

2008: 59.8%
2014: 57.0%
2019: 52.4%
2023: 47.8%
2024: 47.0%

That’s happening even as average fastball velocity continues to increase. But fastballs, no matter how hard they’re thrown, get hit — at least more than other pitches. Check out the numbers from 2023:

All fastballs: .269/.354/.447
Curveballs: .224/.274/.372
Sliders/sweepers: .220/.275/.379
Changeups: .239/.287/.381
Cutters: .269/.333/.448

“I think every pitch we make is a business decision,” Bailey said. “These guys are competing to provide income and to obviously play a game at the end of the day, but this is their livelihood, and if they do well, the Red Sox do well, and we win and get to the playoffs. So every pitch we throw is a business decision to make a bet to suppress damage or induce swing-and-miss.”

You can see that mentality in the changes in approach from individual Red Sox pitchers, especially the starters.

Houck has ditched a four-seamer he threw nearly 10% of the time last season — which batters hit .325 and slugged .550 against — and started throwing his splitter more often. His overall fastball rate has dropped 9 percentage points. He has a 1.99 ERA; his strikeout rate has increased 4 percentage points while his walk rate is down 5.

Batters hit just .163 against Crawford’s four-seamer last season, but he’s still throwing it 10% less often in favor of a big increase in his sweeper usage and a slight increase in his splitter. His strikeout and walk rates have held steady, but his hard-hit rate has improved from the 76th percentile to the 95th percentile, resulting in a lower home run rate. His 1.56 ERA through seven starts ranks second in the majors.

Whitlock threw a sinker 53% of the time last season and batters hit .326 and slugged .538 against it. In his four starts before his injury, he added a slider and cutter and dropped his sinker usage to just 22.7%. He has a 1.96 ERA in his limited time. Bello has a 3.04 ERA in five starts after scrapping a four-seam fastball that he threw 21% of the time and which batters hit .310 and slugged .646 off in 2023, now sticking with a three-pitch mix, throwing his changeup and slider more often to go with his sinker.

“I don’t really say that it’s we don’t want to throw fastballs,” Bailey said. “It’s just they don’t produce as great of outcomes as off-speed pitches in general — and some guys have unicorn fastballs. We just want guys to know their identity as a pitcher and use that to their strength.”

The initial talks between Bailey and the pitching staff surrounding a change in approach began in the offseason. Red Sox players took quickly to the message upon arriving at spring training.

“If you know that a certain pitch type is going to outperform another and you can throw that in the zone, why wouldn’t you want to throw that more often than not?” Bailey said.

Finding what to replace the fastball with is essential. For Houck, a splitter he is throwing twice as frequently as a season ago has become an option after he improved it this offseason. A slight grip change has added a little more depth and north-south movement to it, but Houck has also simply grown more confident in using it. Batters hit .310 against the splitter last season, but are hitting .208 without a home run against it in 2024.

“I think my splitter is better than it’s ever been, so I feel more comfortable throwing it any count, where in the past maybe I’d throw a fastball,” he said.

No matter the pitch, an important key for the Red Sox is still strike one and “pounding the zone relentlessly,” as Bailey put it. With fewer fastballs, that means pitchers have to throw breaking balls or off-speed pitches often enough for strikes rather than simply as chase pitches, otherwise batters will eventually adjust to take those pitches for balls and get ahead in the count — forcing pitchers to come in with a fastball that might not be their best pitch.

In the first pitch of a plate appearance, MLB pitchers throw a fastball 51% of the time in 2024 — slightly more often than overall. There can be a price to pay for that, however: When batters put the first pitch in play in 2024, they’re hitting .327 with a .544 slugging percentage. The Red Sox throw a first-pitch fastball just 34.2% of the time, yet they’re still getting a first-pitch strike 62% of the time — a hair above the MLB average. And when the first pitch is in play, Red Sox pitchers have allowed the third-lowest OPS, behind only the Los Angeles Dodgers and Seattle Mariners.

Maybe it’s not quite a revolution, but it’s certainly different from any team we’ve seen before.

“Anytime you stand off on a limb and challenge the norms of what we do …” Bailey started to say, and then paused. “It’s not really challenging the norms. I want our pitchers to succeed. I want them to be the best versions of themselves. I want them to be happy and excited and purposeful and fulfilled. When you look at things through an analytical lens, then you can build a relationship with a player and provide them the support they need to become that best version. You’re just educating them on what they do well and what makes them an outlier relative to the league.”

Breslow is quick to point out that this could just be a moment in time, that in a couple months, maybe the percentages will have changed. Baseball is, after all, a game of adjustments. There is no doubt, however, that the Red Sox are the extreme case of the fewer fastballs movement. Just as every team eventually joined the shift revolution, perhaps in five years every team will be throwing 32% fastballs.

For now, the approach has helped Red Sox pitchers to an extraordinary start that has kept the team over .500 despite all the injuries, a makeshift roster — and one crowded clubhouse.