The Physics of Pitching Velocity and Strikeouts

Pitching velocity, measured in miles per hour (mph), is more than just a number on a radar gun. It directly influences the reaction time a hitter has. A pitch thrown at 95 mph reaches home plate in roughly 0.45 seconds, while a 98 mph fastball cuts that to about 0.43 seconds. That tiny difference can be the gap between a swing and a miss. For deGrom, higher velocity means his fastball appears to explode or “rise” (due to backspin) while also limiting a batter’s ability to adjust to off-speed pitches. In short, velocity magnifies the effectiveness of his entire arsenal.

Studies from FanGraphs and Baseball Savant have repeatedly shown a strong correlation between higher fastball velocity and increased strikeout rates across MLB. For a pitcher like deGrom, whose fastball has consistently ranked among the elite, this relationship becomes even more pronounced. However, velocity alone doesn’t guarantee strikeouts — location, movement, and sequencing matter. deGrom’s ability to combine elite velocity with pinpoint command and a devastating slider has made him a strikeout machine.

Tracking deGrom’s Velocity Evolution

To understand how velocity influenced deGrom’s strikeout rates, it helps to break down his career into distinct phases. Each phase shows how his fastball speed shifted — due to health, mechanics, or intentional adjustments — and how those shifts impacted his ability to miss bats.

Rookie Season (2014)

deGrom debuted at age 26, an older rookie who had already undergone Tommy John surgery in college. In 2014, his fastball averaged around 94.7 mph, but its explosive life made it appear even faster. He posted a strikeout rate of 9.2 per nine innings (K/9), a strong rookie campaign. Already, his velocity separated him from league average, which sat at about 92 mph. His four-seam fastball generated whiffs at a 10.5% rate, a precursor to the dominance to come.

Rise to Stardom (2015–2017)

From 2015 to 2017, deGrom’s velocity increased. His average fastball climbed to 95.8 mph in 2015 and stayed near 95.5 mph through 2017. During those three seasons, his K/9 rose from 8.9 to 10.7, then to 10.0. Notably, 2016 saw a temporary dip in velocity due to a lat strain, and his strikeout rate correspondingly fell to 8.9 K/9 that year. The pattern was clear: when deGrom threw harder, he struck more batters out. By 2017, his fastball whiff rate had climbed to 12.9%, and his strikeout rate followed suit. He also began to develop a slider that became a key complement to his fastball.

Peak Years (2018–2019)

These two seasons represent the apex of deGrom’s velocity-strikeout relationship. In 2018, his fastball averaged a career-best 97.0 mph, and he posted a stunning 11.2 K/9. He won the first of two consecutive Cy Young Awards. The following year, his velocity remained elite at 96.8 mph, and his K/9 actually increased to 11.3. During this period, deGrom led the league in strikeout rate and whiff percentage. His slider and changeup became nearly unhittable because hitters had to respect the 97–98 mph heater. The synergy between velocity and secondary pitches was at its peak.

Injury Setbacks (2020–2023)

The 2020 season was shortened by the pandemic, but deGrom’s velocity remained high — averaging 97.7 mph, the highest of his career. He posted a 13.8 K/9 in just 68 innings, showcasing what he could do when fully healthy. However, injuries began to mount. In 2021, he was dominant when on the mound (12.1 K/9, average velocity 97.0 mph) but missed time with forearm tightness. By 2022, his velocity dipped to 96.4 mph, and he missed significant time due to a stress reaction in his scapula. His K/9 fell to 9.8, his lowest since 2016. The 2023 season was a nightmare: deGrom had only six starts before needing Tommy John surgery, averaging 96.2 mph with an 8.8 K/9. The velocity drop, though still above average, correlated with a notable decline in swing-and-miss ability.

2024 Return and Future

As deGrom works his way back from surgery, his velocity will be closely monitored. Early reports from his rehab suggest his fastball has returned to the mid-90s, but whether he can sustain 97+ mph over a full season remains the central question. The relationship between his velocity and strikeout rates will be the key indicator of whether he can return to his dominant form.

Velocity vs. Strikeout Rate: A Statistical Analysis

To quantify the influence, we can look at deGrom’s career numbers. His average fastball velocity over 10 seasons is 96.1 mph. His career K/9 stands at 10.9. However, the year-to-year variation tells a clearer story:

  • 2014: 94.7 mph → 9.2 K/9
  • 2015: 95.8 mph → 8.9 K/9
  • 2016: 95.2 mph → 8.9 K/9
  • 2017: 95.5 mph → 10.0 K/9
  • 2018: 97.0 mph → 11.2 K/9
  • 2019: 96.8 mph → 11.3 K/9
  • 2020: 97.7 mph → 13.8 K/9
  • 2021: 97.0 mph → 12.1 K/9
  • 2022: 96.4 mph → 9.8 K/9
  • 2023: 96.2 mph → 8.8 K/9

While the correlation is not perfectly linear — other factors like pitch mix and health matter — the trend is unmistakable. In seasons where deGrom’s average velocity was at or above 96.5 mph, his K/9 averaged 11.7. In seasons below that threshold, it dropped to 9.4. That’s a difference of over two strikeouts per nine innings, a massive swing in production.

Whiff Rates and Swinging Strikes

A deeper dive into whiff rates confirms the pattern. deGrom’s swinging strike percentage (SwStr%) has also tracked with velocity. In his peak 2018–2020, his SwStr% was above 16%, league-leading. In 2022–2023, it fell to 13.1%, still good but not elite. His fastball whiff rate dropped from over 20% to under 16%. Without that high-velocity fastball to set up his slider and changeup, hitters were able to make more contact. The relationship is causal: velocity creates more swing-and-miss on the fastball itself, and it also makes hitters more aggressive against secondary pitches, increasing their whiff rates as well.

The Role of Secondary Pitches

Velocity alone does not make a strikeout pitcher. deGrom’s slider, which he throws at 88–92 mph with elite horizontal break, is nearly unhittable when paired with a 97+ mph fastball. His changeup, used mainly against left-handed hitters, also benefits from the velocity gap. When his fastball lost a couple ticks, the break of his slider appeared less extreme, and hitters could lay off or foul off more pitches. The interplay between velocity and secondary effectiveness is a key reason why deGrom’s strikeout rates are so sensitive to his fastball speed.

According to MLB.com, deGrom’s slider whiff rate in 2020 was over 55%, the best in baseball. That year, his fastball averaged 97.7 mph. In 2023, his slider whiff rate dropped to 41%, while his fastball sat at 96.2 mph. The difference may seem small, but in pitcher-hitter duels, a 2-mph reduction can change a slider from an automatic whiff to a foul ball.

Comparisons to Other Elite Pitchers

deGrom’s story is not unique in modern baseball. Other high-velocity pitchers like Justin Verlander, Gerrit Cole, and Spencer Strider have shown similar correlations between their fastball speed and strikeout rates. However, deGrom’s reliance on velocity is particularly pronounced because his pitch mix — heavy on fastballs and sliders — does not include a sinker or cutter that might provide a different look. For pitchers with more diverse arsenals, velocity dips may be masked. deGrom’s approach is more linear: if the fastball velocity falls, his entire arsenal becomes less effective.

A FanGraphs analysis of deGrom’s career compares his velocity-induced strikeout gains to those of peak Pedro Martinez, who relied more on movement and location. While Martinez had a lower average velocity, he maintained elite strikeout rates into his 30s because his secondary pitches were less velocity-dependent. deGrom, at 36, faces a different challenge: he needs to either maintain elite velocity or adapt his repertoire to sustain his strikeout dominance.

Injuries and Their Effect on Velocity

Injuries are the primary driver of deGrom’s velocity fluctuations. His two Tommy John surgeries (one in college, one in 2023) and various other arm ailments have each caused measurable dips. The lat strain in 2016, the forearm tightness in 2021, and the scapula stress reaction in 2022 all led to velocity drops of 0.5–1.5 mph. Those dips, while small in absolute terms, significantly impacted his strikeout output. The challenge for deGrom post-surgery will be whether his right elbow can withstand the torque required to generate 97+ mph fastballs. If he can, his strikeout rates could return to peak form; if not, he may need to pitch more like a crafty veteran — relying on command and spin rather than raw heat.

Mechanical Adjustments and Training

Beyond injuries, deGrom has tweaked his mechanics over the years to maximize velocity and health. During his peak, he employed a more aggressive hip-shoulder separation and a slightly higher arm slot, which allowed him to generate more force through the ball. After his 2021 forearm issues, he notably changed his warm-up routine and simplified his delivery to reduce stress on the elbow. These adjustments have yielded mixed results: while they helped him return to the mound quickly, they also contributed to a slight reduction in his natural velocity. Biomechanical studies from Driveline Baseball suggest that even small changes in trunk tilt and arm angle can impact both velocity and spin rate. For deGrom, maintaining optimal mechanics will be just as important as pure strength in preserving his fastball speed.

The Mental Side of Velocity

Pitching with elite velocity also affects a pitcher’s mentality — and by extension, his effectiveness. When deGrom is throwing 97-98 mph, he pitches with confidence, attacking the strike zone with the knowledge that hitters are on the defensive. Hitters themselves become more passive, swinging earlier in counts and taking fewer risks. This psychological edge amplifies his strikeout numbers. Conversely, when his velocity dips, deGrom has admitted to feeling less dominant, leading to more nibbling and fewer swings in favorable counts. Data from Statcast shows that in 2023, deGrom’s first-pitch strike rate fell by 3% compared to 2020, and hitters swung at pitches outside the zone less often. The connection between velocity, confidence, and strikeout rate is a subtle but real factor in his career arc.

The Future of deGrom’s Velocity

As deGrom enters the later stages of his career, the question becomes how long he can maintain high velocity. Historical comparisons show that most pitchers lose 1–2 mph by their mid-30s, even without major injury. deGrom’s 2023 season was essentially lost to surgery, so his 2024 return will be a crucial data point. If he can sustain 95–96 mph, he may still be a top-tier strikeout pitcher. If his velocity falls to 93–94 mph, his K/9 could drop below 9.0, making him a solid starter but no longer the elite dominator he once was.

Advances in training and analytics may help. Pitchers today use weighted ball programs, biomechanical analysis, and targeted strength work to preserve velocity. deGrom has access to the best resources with the Texas Rangers. However, the human body has limits. The most likely scenario is that deGrom’s velocity will continue to trend downward gradually, and his strikeout rates will follow, at least to some degree.

Conclusion

Jacob deGrom’s career arc illustrates the direct and powerful influence of pitching velocity on strikeout rates. From his rookie season through his peak, higher fastball speed consistently correlated with higher strikeout numbers. When injuries caused velocity dips, his ability to miss bats diminished. This relationship is not unique to deGrom, but his extreme reliance on velocity — combined with the elite level of his fastball — makes him a perfect case study. As he works to return from his second Tommy John surgery, the baseball world will be watching his radar gun readings as the primary indicator of whether his strikeout magic will return. The numbers are clear: for deGrom, velocity is not just a tool — it is the engine of his dominance.