Major League Baseball recently released a report about pitcher injuries, which was the culmination of interviews with 200 subject-matter experts about the growing rash of arm troubles in the sport. The report includes entire sections about the concept of stuff metrics, like Stuff+, and how they may relate to pitcher health.
What is Stuff+?
Aptly named, Stuff+ is a number that evaluates a pitcher by studying his movement, velocity, spin, and release points. It’s generally trying to remove the context of how a specific pitch performed on the field by looking at how certain combinations of shapes, velocities, and spins usually perform across baseball and then assigning that value back to the pitch itself. What started with a revelation like “hard sliders that drop a lot are good” has become more complicated, but the analysis comes from the same place.
Pioneers of Stuff+
Pioneered by former Cubs research and development analyst Jeremy Greenhouse in 2009, the framework and concepts within were pushed forward by analysts like Harry Pavlidis at Baseball Prospectus and many others in the field, including Alex Chamberlain with FanGraphs and Tom Tango with Major League Baseball.
How Does Stuff+ Work?
Working with Ethan Moore, we debuted a Quality of Stuff metric here at The Athletic in 2020 before Max Bay (now with the Dodgers) brought Stuff+ here a year later and eventually on to FanGraphs, where it now lives in a sortable leaderboard. Driveline Baseball first posted about its model, built by now-Phillies R&D head Dan Aucoin, in late 2021 but had already been using it before it went public. Now there are many competing models available publicly, and most teams have their own private versions.
Velocity is Good
The most basic and powerful pillar of Stuff+ is that velocity is good. That’s no surprise, but it’s not just that the velocity of the fastball is good for itself. The velocity of the fastball is also good for the secondary pitches, which we define off the fastball using velocity as the “anchor.” This is because hitters have to time the fastball — they have to be able to swing early and hard enough to hit the pitch that is still the most common in baseball. When they do so, they open themselves up for mistakes and swings and misses.
The Impact of Stuff+ on Pitcher Injuries
Despite the link between Stuff+ and injury rates, the research linking specific aspects of stuff and injury rates is a little murkier. For certain, velocity has a huge role. But is it how close a pitcher throws to their own personal maximum, as Glenn Fleisig found in his peer-reviewed study? Then why does a bigger velocity gap not lead to better health outcomes?
Or is velocity generally a stress on the elbow, as Driveline found? And if 80 mph sliders are fine, but 90 mph sliders are actually more stressful, as at least one study found, then maybe breaking ball velocity is one of the biggest strains on elbows?
What’s Next?
Not everyone likes Stuff+, of course, beyond those linking it to injury. “You can never get pitching into one number,” said Max Scherzer about the stat. “Even if you are able to, you’re still missing something.”
The effort to quantify aspects of pitching that stuff metrics miss is well underway despite his skepticism. Driveline (with Mix+ and Match+) and Baseball Prospectus (with its recently released arsenal stats) have attempted to put a number on the value of having wide arsenals with different movement and velocity profiles. Over at FanGraphs, Michael Rosen did some work on release angles that might better quantify command.
“If you cannot measure it, you cannot improve it,” as Lord Kelvin, the legendary physicist, once proclaimed.
That said, every time analysts make an advancement that spreads throughout the game, like Stuff+, it quickly ceases to be an advantage. Boddy thought that 28 of 30 teams had their own internal Stuff+ model, and other analysts agreed that he wasn’t far off.
So maybe the future is more about the exciting research being done in biomechanics that could set a team apart. Over at NTangible, they feel they’ve built a better test of makeup — the attitude and energy that fuels the most successful players — which is notoriously difficult to define, scout, and measure. At the winter meetings, people from all parts of baseball emphasized soft skills as a way to successfully bridge the gap between data and play on the field.
Despite the urge to quantify everything, there’s also the truth that the unquantifiable will always be important, and will remain a possible edge for a team that understands it best (including finding a way to quantify it). These more nebulous aspects of the game will always be a source of chaos in the machine of any metric. And that’s a good thing — it’s a sport, not a simulation.
Conclusion
Stuff+ has revolutionized the way we evaluate pitching, but its impact on pitcher injuries is a more complex topic. While the link between velocity and injury is clear, the exact relationship between stuff metrics and injury rates is still being studied. As researchers continue to work on improving their models, the sport will have to adapt and find new ways to balance the benefits of advanced analytics with the importance of human factors like attitude and energy.
FAQs
Q: What is Stuff+?
A: Stuff+ is a number that evaluates a pitcher by studying his movement, velocity, spin, and release points.
Q: How does Stuff+ work?
A: Stuff+ uses a combination of movement, velocity, spin, and release points to evaluate a pitcher’s stuff, which is then used to assign a value to the pitch itself.
Q: What is the relationship between Stuff+ and pitcher injuries?
A: The research linking specific aspects of stuff and injury rates is a little murkier, but velocity has a huge role. However, the exact relationship between stuff metrics and injury rates is still being studied.
Q: What’s next for Stuff+?
A: The future of Stuff+ is uncertain, but it is likely that it will continue to evolve and adapt to new research and advancements in the field.