Dealing with Dead Zone Part 2: Redefining Dead Zone
Last fall, I published a blog looking into how fastballs in the “dead zone” performed in college baseball. In that analysis, I used the standard definition of the dead zone, a pitch with approximately equal induced vertical and horizontal break. The results showed that, overall, these fastballs performed worse than others unless there is an outlier trait to them, such as velocity. You can read the entire analysis here.
I concluded the last article with a thought of redefining the dead zone. After watching last season in college baseball unfold, I noticed pitchers still performed well despite being in the dead zone. One example of this was Iowa’s Duncan Davitt. His fastball averaged 11 inches of vertical break and 9 inches of horizontal break. Despite being classified as dead zone, he was one of the most effective pitchers on Iowa’s team last year. In this article, I take a deeper dive into how pitchers still performed well even when they classify in the dead zone according to their induced vertical break and horizontal break.
Defining a New Dead Zone
Instead of focusing solely on movement, I wanted to take into account what the hitter would expect when seeing a pitch. Depending on how the pitcher’s arm deploys, the hitter sub-consciously expects a certain movement profile. For example, a pitcher with a higher arm slot would likely have more vertical break on his fastball and less horizontal break. For a sidearm pitcher, we expect there to be more horizontal break than vertical break. The graph below showcases how a pitcher with a higher arm slot would have a dead zone with more induced vertical break compared to horizontal break according to Stuff+. The blue area denotes poor stuff, while red is more favorable.
In order to accomplish this, I built a model that predicted spin axis given the pitcher’s release height and release side on a given pitch. For each pitch, I used the model to calculate an expected spin axis. Spin axis describes the axis the ball spins around as it travels to the plate and is a value in degrees that ranges from 0 to 360. It is directly related to spin direction, so a fastball with a 12:00 spin direction would have a spin axis of 180 degrees. For right-handed fastballs, the value is generally between 190 and 235 degrees, or a 12:30 to 2:00 spin direction.
After this was done, I compared this expected axis to the actual spin axis of the pitch. The difference between those two values could be used to define the new dead zone. The closer the difference was to zero, the more the pitch moved like a hitter would expect, according to the arm slot. If there was a large difference between the two values, the pitch would be further from the dead zone and more unique. From this point on, I will refer to the difference between the expected and actual spin axis as spin deviation.
Results
The first thing I wanted to do was take a look and see if there was any validity to this new dead zone. I plotted some performance metrics against the spin deviation of each pitch in the dataset. In this first plot, I take the absolute value of the difference to see if there was any trend.
There is a clear pattern in this graph. The more a pitch moves like expected, the worse it performs. As the spin deviation increases, there is a sharp increase in chase and whiff rate, wOBACON, and Stuff+.
Deeper Dive into Deviation
Now that we can see there is a clear decline in performance for pitchers who have little-to-no spin deviation, I want to look at the difference between a positive difference and a negative difference. To do this, we need to understand what a positive difference is versus a negative difference.
A positive difference would indicate that the pitcher’s spin axis is greater than the expected axis. In simpler terms, it means the pitcher gets more horizontal break (run) on the fastball compared to what is expected. A prime example of this from college baseball last year was Purdue’s Eric Hildebrand, who averaged a spin deviation of almost 45 degrees. For a negative difference, the pitcher would get more positive vertical break (ride) than expected. This is where Duncan Davitt fell, helping him get selected in last year’s draft.
Looking at the graph above, we see the same trend near zero deviation as was seen in the first graph. As deviations go further away from zero, the performance across all metrics increases drastically. The interesting note about this graph is that the minimum values for whiff and stuff, and the maximum value for wOBACON appear on the positive deviation side. This means that the fastballs that perform the worst according to those metrics are actually those that have slightly more horizontal break than expected. This is another aspect that warrants further investigation in the future.
Merging Both Dead Zones
Using this new methodology of how the dead zone is defined, I wanted to look into how pitches that are defined as dead zone in my previous article compared to how I define dead zone now. I filtered to fastballs that had vertical and horizontal breaks within three inches of each other and plotted the same performance metrics.
The results speak for themselves. Using just the movement differential to define the dead zone is not entirely accurate. If pitchers have similar vertical and horizontal break numbers, but a unique arm slot (e.g. sidearm, over the top), they would no longer be classified as a pitcher with a dead zone fastball.
It can be inferred that the old definition of dead zone is only reliable when the pitcher has a traditional three-quarter arm slot. It seems to be much more beneficial to have a negative spin deviation with more ride than expected. This helps explain why Cooper Hjerpe was so dominant for Oregon State last season that ended with him being selected in the first round of the MLB Draft.
Controlling for Velocity
In my previous blog, I mentioned that a dead zone fastball can still be successful as long as there is an outlier characteristic like above average velocity. I wanted to see if this trend can still be observed with the new definition.
For both figures, there is a distinct performance drop when spin deviation is near zero. With average velocity, favorable results can still be achieved with high spin deviation. For above average velocity, the same trend exists, however the floor for the results is higher. For example, the lowest Stuff+ score for average velocity with spin deviation close to zero is about 70. With above average velocity, the lowest score is slightly above 100. Overall, it is better to have above average velocity, but the best results still come with high spin deviation.
Conclusion
Throughout this article, there has been more than enough evidence to support the claim that the fastball dead zone is dependent on more than just movement alone. Pitchers who are more over the top would have a dead zone with more induced vertical break and less horizontal (example: 14 inches induced vertical break, 9 inches horizontal break). Three-quarter pitchers would maintain the traditional definition of dead zone with equal amounts of vertical and horizontal break. Lower three-quarter and sidearm pitchers would have a dead zone with more horizontal break than induced vertical break (example: 9 inches induced vertical break, 14 inches horizontal break).
So why does this matter? This is a piece to solving the puzzle of deception in pitching. Explaining how pitchers perform well despite having no outlier metrics will give a massive edge in recruiting, scouting, and development. At Iowa, we have incorporated this concept into our stuff model, and it has changed how we value pitchers’ fastballs. Understanding the more intangible parts of the game, like how hitters think and what they expect is what makes this metric important and valuable. Numbers can drive a lot of development, but mixing it with an understanding for the game and the mental side drives new ideas.
This further helps coaches and players understand their arsenals and expands the ways that pitchers can be effective without outlier movement or velocity. Just because a pitcher has equal amounts of induced vertical and horizontal break does not mean they should be thought of as a pitcher that cannot be effective. Using this information can help teams find undervalued players and turn them into great college pitchers.
