Jacob deGrom is widely regarded as one of the most electrifying and dominant pitchers in Major League Baseball history. With a fastball that routinely touches triple digits, a slider that defies physics, and a changeup that leaves hitters frozen, the two-time Cy Young Award winner has carved a reputation as a once-in-a-generation talent. Yet over the past several seasons, even a pitcher of deGrom's caliber has seen fluctuations in his performance that defy simple explanation. Some of these shifts can be linked to injuries and age. But a growing body of evidence suggests that changes in the composition of the baseball itself have played a significant—and often overlooked—role in altering the trajectory of deGrom's career.

Since 2021, Major League Baseball has made substantive modifications to how its baseballs are manufactured. The stated goal was to standardize quality and manufacture, but these changes have inadvertently affected the ball's liveliness, grip, and flight characteristics. For a pitcher like deGrom, whose game relies on elite velocity, sharp movement, and pinpoint command, even subtle differences in the baseball can translate into tangible shifts in performance. This article explores the evolving science of the MLB baseball, how those changes have impacted deGrom’s key pitches, and what the data reveals about his performance before and after the alterations.

The Evolution of MLB Baseballs: A Brief History

Baseballs are not static objects. Despite appearing nearly identical to the naked eye, major league baseballs have undergone several transformations over the past decade. The modern baseball manufacturing process involves winding wool and cotton around a cork-and-rubber core, then wrapping it in a leather cover stitched with 108 double stitches. However, the precise materials, tension, and processing methods have changed.

In 2015, MLB began producing balls with slightly lower seams after a manufacturing shift at the Rawlings plant in Costa Rica. The goal was consistency, but the result was a ball that carried farther, leading to the infamous "juiced ball" era from 2015 to 2019, where home run rates skyrocketed. Then, prior to the 2021 season, MLB introduced a new ball that appeared to be deader—lower coefficient of restitution (COR), slightly higher weight, and a different feel. This "dead ball" period was later refined in 2022 and 2023 as the league attempted to strike a balance between offense and the integrity of the game.

According to a 2021 MLB press release, the league stated that the new ball would "return to the specifications used in previous years," following concerns about inconsistencies. However, independent testing by researchers at the University of Massachusetts and other institutions found that the 2021 balls were indeed different: slightly larger, with a lower COR and seam heights that varied more than in previous years.

The 2021 Dead Ball Era and Beyond: Measurable Differences

The league's stated intention was to reduce home run rates and restore some balance between pitchers and hitters. But the effect on pitchers was more complex. The 2021 baseball was found to be about 0.5 grams heavier, with a COR that dropped from about 0.515 to 0.510. While that sounds minimal, in a game where a tenth of an inch of movement or a fraction of a mile per hour can mean the difference between a swing and a miss and a home run, it matters significantly.

Moreover, the seams on the 2021 balls were raised slightly compared to the 2020 balls, which initially sounds like it would benefit pitchers. However, the inconsistency in seam height across individual balls—some with high seams, some with nearly flat seams—made it harder for pitchers to achieve consistent grip and spin. A Baseball Reference analysis noted that the variance in seam height from ball to ball in 2021 was the highest recorded in the Statcast era.

By 2022, MLB made another tweak, reducing the seam height variance and standardizing the ball further. Yet pitchers across the league continued to report differences in feel and performance. For Jacob deGrom, who returned from injury in mid-2021 and then made only 11 starts in 2022, the changes coincided with a period of both physical rehab and adaptation to a new baseball.

How Ball Composition Affects Pitches: Physics and Feel

Understanding how a baseball's construction influences pitching requires a brief dive into physics. The interaction between a pitcher's fingers and the seams creates the spin that dictates movement. A higher seam allows the pitcher to create more friction, generating higher spin rates and more "bite" on breaking pitches. Conversely, a flatter seam reduces friction, causing the ball to slip more, leading to lower spin and less movement.

The weight of the ball also matters. A heavier baseball requires slightly more energy to accelerate, and though the difference is small, it can affect release velocity. More critically, a heavier ball tends to carry less through the air, reducing the "hop" on a four-seam fastball—the illusion of the ball rising as it approaches the plate. The deadened ball also leads to lower exit velocities off the bat, which can help a pitcher's ERA but also changes how a pitcher approaches hitters.

For a pitcher like deGrom, his four-seam fastball is his bread and butter. It sits 97-99 mph and can touch 101, but its true weapon is the vertical approach angle—the rising action that causes hitters to swing under it. When the ball's aerodynamics change, that rising effect diminishes. Similarly, his slider, which sweeps across the zone with late horizontal break, relies on high spin efficiency. Any drop in spin efficiency or seam-shifted wake effects can flatten the pitch, making it more hittable.

In a 2021 interview, deGrom himself noted that "the ball feels different this year. It’s harder to get the same grip, especially when it’s humid. Some balls are slick, some are tacky." His comments mirrored those of other elite pitchers, including Gerrit Cole and Max Scherzer, both of whom publicly voiced concerns about the consistency of the baseball during that period.

Jacob deGrom's Pitching Arsenal: A Diamond in the Rough

DeGrom's success is built on three primary pitches: a four-seam fastball, a slider, and a changeup. He also mixes in a curveball and an occasional sinker, but the core three account for the vast majority of his pitches since 2019. Each pitch has its own relationship to the baseball's construction.

  • Four-Seam Fastball: DeGrom’s fastball is elite not just for velocity but for its induced vertical break (IVB). In his Cy Young seasons (2018 and 2019), his IVB averaged around 18-19 inches, well above the league average. That high IVB creates the "rising" effect that induces whiffs. Starting in 2021, his IVB dropped to about 16-17 inches, a significant decline that correlates with the dead ball era.
  • Slider: His slider is a sweep-heavy pitch with horizontal break around 10-12 inches and vertical drop around 3-4 inches. In 2021 and 2022, scouts noted that the pitch looked "flatter" at times, and Statcast data confirms that his slider’s vertical movement dropped by about 1.5 inches on average. The reduced seam friction likely contributed.
  • Changeup: DeGrom’s changeup is a plus pitch, but it relies on arm speed deception and a little tumble. The change in ball weight may affect the changeup's movement less than the fastball or slider, but the overall command of the pitch suffered as deGrom struggled to grip the ball consistently, leading to higher walk rates.

Statistical Breakdown: deGrom's Performance Before and After the Ball Change

To isolate the effect of the ball change, we can compare deGrom’s performance from his peak years (2018-2019) with the period from 2021-2023, excluding his injury-riddled 2020 and partial 2021 season to focus on his active periods.

Statistic 2018-2019 (Pre-Ball Change) 2021-2023 (Post-Ball Change)
ERA 1.94 2.38
FIP 2.02 2.60
K/9 11.6 12.8
BB/9 1.9 2.9
HR/9 0.6 0.8
Fastball Velocity (avg) 98.3 mph 97.5 mph
Fastball IVB (in) 18.2 16.8
Slider Whiff% 47.3% 39.1%
Hard Hit% allowed 29.4% 32.1%

The trends are clear: while deGrom’s strikeout rate actually increased slightly in the post-change period (likely due to hitters being less able to adjust to his mixes, plus a change in approach), his walk rate jumped by over a full walk per nine innings. His home run rate increased, and his fastball lost both velocity and vertical movement. The drop in IVB is especially concerning because it correlates with a drop in whiff rate on the fastball from 34% to 28%. Hitters were making more contact, and more solid contact, resulting in a higher hard-hit rate.

These changes are not all attributable to the ball alone—deGrom also dealt with elbow and shoulder injuries that forced him to alter his mechanics and pitch mix. But the timeline of the ball change aligns precisely with the statistical shifts, and the nature of the changes (reduced movement, lower IVB, higher walks from grip issues) is exactly what pitchers reported about the new baseballs.

Velocity Decline: Ball Weight or Injury?

One of the most debated aspects is whether deGrom's slight drop in velocity (from 98.3 to 97.5 mph, roughly 0.8 mph) is due to the ball or to accumulating injury history. Studies have shown that even a 0.5-gram increase in ball weight can reduce exit velocity by about 0.2 mph on average for a pitcher, because the pitcher must exert slightly more force to achieve the same release speed. Over a full season, that might account for a 0.3-0.5 mph drop. The remainder of the decline likely stems from deGrom's altered mechanics and the accumulated stress of injuries.

However, velocity alone is not the story. More important is how that velocity is applied. DeGrom's fastball in 2021 and 2022 was not only slower but also lacked the same "hop" at the end. That hop, or induced vertical break, is a product of spin rate and seam orientation. With the dead ball, the spin rate on deGrom's four-seamer actually remained high (around 2,500 rpm), but the efficiency of that spin dropped—meaning more of the spin was sideways rather than vertical. That suggests the ball's seams were not providing the same grip, causing the ball to orient differently in flight.

The Human Factor: deGrom's Own Words and Adaptation

DeGrom has never been overly expressive about external factors, preferring to focus on his own execution. But in several interviews during the 2021 and 2022 seasons, he acknowledged that "the baseball is a little different" and that he had to make adjustments. In spring training 2022, he told reporters that he was "still getting used to the feel of the ball" and that "some days it's good, some days it's not."

His teammate at the time, Marcus Stroman, was more direct, tweeting about the inconsistency of the baseballs and how it affected pitchers' ability to grip and spin the ball. The league, in response, implemented a humidor system in 2022 to store baseballs at a consistent humidity, which helped reduce variance in feel. Yet even with the humidor, deGrom's spin efficiency on his fastball never fully returned to its 2018-2019 levels.

The psychological effect should not be underestimated. A pitcher who feels he cannot trust his grip or his movement may begin to nibble more, leading to deeper counts and more walks. DeGrom's walk rate jump from 1.9 to 2.9 per nine suggests that he was indeed more tentative. His zone rate—percentage of pitches thrown in the strike zone—dropped from 48% to 44% over the same period. When he did attack the zone, hitters were able to make more contact, in part because the movement was less extreme.

Comparisons to Other Elite Pitchers: A League-Wide Trend

deGrom is not alone. Across the league, elite pitchers experienced similar declines in spin efficiency and movement after the ball change. Gerrit Cole's fastball IVB dropped from 17.5 inches in 2019 to 16.0 inches in 2021. Max Scherzer saw a drop in his slider vertical break. Justin Verlander's strikeout rate dipped slightly, and his walk rate increased.

A Bloomberg investigation in 2021 analyzed Statcast data across the league and found that the average fastball IVB dropped by about 0.8 inches from 2020 to 2021, and the average curveball vertical movement dropped by 1.2 inches. These are league-wide effects that cannot be explained by individual pitcher injuries alone.

The consistency of this trend across different pitchers and teams strengthens the argument that the ball itself is a primary driver. deGrom's particular sensitivity may stem from his reliance on vertical movement. Pitchers like Cole or Scherzer have more horizontal movement in their arsenals, which was less affected by the dead ball, so their statistical declines were less dramatic. For deGrom, whose fastball is almost entirely vertical in its action, the loss of IVB was a direct blow to his most important pitch.

Injury Context: How Ball Changes May Affect Arm Health

An often-overlooked aspect of ball composition changes is their potential impact on injury risk. When a baseball feels different—slicker, heavier, or with inconsistent seams—a pitcher may subconsciously alter his grip pressure or arm slot to compensate. Over time, these small compensations can lead to mechanical inefficiencies that increase stress on the elbow and shoulder.

deGrom’s injury history is well documented: he missed significant time in 2021 with forearm tightness and later underwent Tommy John surgery in 2023. While his injuries likely stem from the violent nature of his delivery and years of high-intensity pitching, some analysts have pointed out that the shift to a different ball could have contributed to the final breakdown. When a pitcher loses feel for his pitches, he may try to "do too much" with his arm, using more force to generate the same movement, leading to increased torque on the ulnar collateral ligament.

A Sports Illustrated article in 2022 explored this connection, citing a study that found pitchers who threw with the new baseball reported higher rates of forearm and elbow discomfort. Though not definitive, the correlation aligns with the timeline of deGrom's injury troubles.

Looking Ahead: What Future Ball Changes Mean for deGrom

MLB continues to tinker with the baseball. In 2023 and 2024, the league has made additional modifications to seam height and tackiness, attempting to give pitchers more consistent feel while still limiting home runs. deGrom, now rehabbing from Tommy John surgery and expected to return in 2025 or 2026, will face another transition when he returns. However, the league is now more aware of the impact of ball changes, and the manufacturing process has become more refined.

If deGrom can return to full health, his ability to adapt to the current baseball will be crucial. He has shown before that he can adjust—his 2022 start (11 starts) included a 3.08 ERA with a 14.3 K/9, suggesting he had begun to find his feel again, even with the dead ball. But the long-term sustainability will depend on his arm holding up and the ball remaining consistent.

For fans and analysts, the story of Jacob deGrom's performance changes serves as a case study in how even the smallest equipment modifications can ripple through a sport. The ball is not just a ball—it is a dynamic piece of engineering that interacts with the pitcher's skill in ways we are still discovering.

Conclusion

Jacob deGrom's performance fluctuations over recent seasons cannot be reduced to a single cause. Injuries, age, and mechanical changes all play parts. But the evidence is strong that the changes in MLB ball composition that began in 2021 have had a measurable and meaningful effect on his pitching. From reduced fastball vertical movement to a decrease in slider effectiveness, from higher walk rates to altered spin efficiency, the dead ball era has posed a real challenge to one of the game's greatest arms.

As baseball continues to evolve, both the sport's governing bodies and its athletes must remain alert to the unintended consequences of even well-intentioned rule changes. For Jacob deGrom, understanding how the ball affects his craft may be the key to returning to his Cy Young form. For the rest of us, it is a reminder that baseball's beauty lies in its complexity—a game where the object itself can shift the balance of power in invisible but undeniable ways.