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For the Red Sox, the timing of a woeful pitching stretch is suspicious. The spin rate data is not.

On June 3, shortly after Martín Pérez concluded a gem against the Astros, MLB informed owners that it planned to crack down on the use of foreign substances by pitchers. Before that revelation, the Sox had a middle-of-the-pack 3.92 ERA and 4.04 starters’ ERA in 56 games. In 10 games following (prior to Monday night), the Red Sox had a 6.13 ERA (fourth-worst in MLB) and an 8.20 ERA from their rotation (2nd worst).

The conclusion seems obvious: The Red Sox were using some sort of spin-generating tacky substance, but stopped once the league decided to restrict such practices, and the team’s performance cratered as a result. Easy, right?

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The problem with that conclusion is such foreign substances are supposed to permit pitchers to achieve incredible, unprecedented amounts of spin to create pitch shapes unlike anything the game has seen.

Such an ability is particularly important for four-seam fastballs at the top of the strike zone — where extra RPMs mean a pitch that appears to jump over where a batter has been trained for his entire life to think it will end up — as well as breaking balls, where spin amplifies movement. Studies about the value of Spider Tack, a glue-like adhesive invented for weight-lifting competitions, suggest that the sticky substance can contribute hundreds of RPMs to fastballs beyond the use of traditional rosin.

(Changeups and two-seam fastballs, by contrast, are offerings in which pitchers look to kill spin in order to create drag and sink.)

Do the spin-rate numbers suggest Red Sox pitchers have changed their behaviors since MLB put owners (and, in turn, pitchers) on notice? Simple answer: No.

There has been virtually no change in the spin rate or movement profiles of any Red Sox starter’s four-seam fastball, curveball, or slider. The most dramatic change has come with Garrett Richards, whose spin rates on his fastball, slider, and curveball have gone up since the league informed owners of its plans.

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A change in spin rate? Not so fast Data show that the pitchers in the Red Sox starting rotation haven't seen a drastic change in spin rate.
Pitcher and pitch type Spin rate pre-June 3 (RPM) Spin rate post-June 3 (RPM) Change
GARRETT RICHARDS
4-seam fastball 2586 2625 1.5%
Curveball 3271 3388 3.6%
Slider 2874 2930 1.9%
NICK PIVETTA
4-seam fastball 2318 2324 0.3%
Curveball 2771 2735 -1.3%
Slider 2308 2266 -1.8%
EDUARDO RODRIGUEZ
4-seam fastball 2175 2173 -0.1%
MARTÍN PÉREZ
4-seam fastball 2167 2146 -1.0%
Curveball 2470 2470 0.0%
NATE EOVALDI
4-seam fastball 2145 2112 -1.5%
Curveball 2142 2178 1.7%
Slider 2192 2168 -1.1%
SOURCE: Baseball Savant

Though Travis Sawchik of theScore found that 37 pitchers had declines of more than 100 RPMs after the decision to start policing foreign substances, no Red Sox starting pitcher had a decline of as much as 50. All of the changes seemed to fall within a normal range of start-to-start variance.

In the two turns of the rotation that followed the decision about foreign substances, every Red Sox starter’s four-seam fastball and, if they throw them, slider and/or curveball registered within two percent of their prior season norms, with one exception. Richards, who has featured one of the highest spin rates in the majors throughout his career, has seen his curveball increase from 3,271 RPMs to 3,388, a 3.6 percent jump.

An analyst from another team suggested that Sox starters continued to throw pitches “that move like they have all year. They’re just throwing them in bad spots and they’re getting hit.”

That, at least, is what the pitch data suggests. Is it possible that a substance other than Spider Tack could improve a pitcher’s command without affecting spin rates? Maybe. Anecdotally, generations of pitchers used pine tar in hopes of better control without much thought to the implications for movement. That said, studies have shown that pine tar has been linked to spin rate increases, just less dramatic ones than those produced by modern adhesives.

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The Red Sox are aware that their recent struggles make for an easy, connect-the-dots conclusion. But they bristle at the suggestion of cheating — or, more specifically, an inability to do so.

Matt Barnes says he isn't buying the easy narrative.
Matt Barnes says he isn't buying the easy narrative.Jim Davis/Globe Staff

“Isn’t that always the easiest answer for everybody? In the steroid era, if someone was good, it was automatically, ‘He’s on steroids.’ You look back to when a team struggles, it’s, ‘They’re not doing this,’ ” said Matt Barnes. “The easiest way to justify someone being bad or good over a stretch is something other than what it really is. It’s just the easiest way to talk about it.

“[Struggle] happens. That’s what happens when you play 162 games in the season. You’re going to have a 10-game stretch where starters struggle. There’s too many games to stay at an elite level for every single one of them,” he continued. “[Blaming foreign substances] just seems like an easy way out.”

Stretches such as the one in which the Sox found themselves entering Monday — a 12.00 rotation ERA over six games — do indeed happen, albeit rarely. The dismal 2020 Red Sox had a 14.21 ERA over a six-game stretch. The 2019 team (featuring Sale, David Price, Eduardo Rodriguez, Rick Porcello, Brian Johnson, and Andrew Cashner) had a 12.24 mark over six contests around the trade deadline. The 2012 team finished the year with a 13.14 rotation ERA in its final six games.

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But timing is everything. Those poor stretches represented indictments of the pitching staff. They didn’t come at a time when MLB decided to pursue a policy that was bound to pique curiosity about who would struggle and who wouldn’t, which pitchers would see their pitch data change and which wouldn’t.

“Any time there’s [a scandal] like [foreign substances], everyone is gonna throw that on there first,” said Sale. “It’s a new excuse so it’s fun — let’s use it. But anybody that actually knows the game and studies the game would see that it’s just a bad stretch. Unfortunately, it’s come in a bulk. You usually have one or two guys struggling at a time and then it will flip flop. . . . We’ve hit kind of a skid where it’s been kind of consecutive.”

On Monday, in a 2-1 Red Sox walkoff win over the Blue Jays, Nate Eovaldi halted that skid with 6⅔ shutout innings. His spin rates barely diverged from his season averages or his marks in his prior two starts. In the wake of a Red Sox win, they were treated as a non-issue.

See more data

Red Sox rotation: Spin rate data None of the pitchers in the Red Sox starting rotation have seen dramatic changes in their spin rate since MLB said it would crack down on the use of substances to enhance grip.
Pitcher Four-seam spin rate (RPM) Pitch % Velocity (mph) Opponents' batting average
Nick Pivetta
April 1-June 3 2318 51.3 94.8 .216
June 4-13 2324 53.7 94.9 .333
Change 0.2% 0.24% 0.1 .117
Garrett Richards
April 1-June 3 2586 56.9 94.1 .270
June 4-13 2625 56.1 94.6 .367
Change 1.5% -0.8% 0.5 .097
Eduardo Rodriguez
April 1-June 3 2175 31.2 92.4 .293
June 4-13 2173 45.4 92.7 .353
Change 0% 14.2% 0.3 .060
Martín Pérez
April 1-June 3 2167 10.7 93.0 .182
June 4-13 2146 6.2 93.3 .000
Change -1% -4.5% 0.3 -.182
Nate Eovaldi
April 1-June 3 2145 44.4 97.0 .299
June 4-13 2114 43.8 97.6 .350
Change -1.4% -0.6% 0.6 .051
SOURCE: Alex Speier

Alex Speier can be reached at alex.speier@globe.com. Follow him on Twitter at @alexspeier.