Is the Ryne Nelson of the second half for real? Is Yilber Diaz a starter? And what the heck happened to Jordan Montgomery? How these questions led me to discovering a new pitch I hadn’t ever even heard of before.
Following the addition of Corbin Burnes, several Dbacks pitchers have come into focus for the backend of a suddenly very deep rotation. I decided to take a deeper dive into some of their arsenals. I was focusing on a couple things: Is the Ryne Nelson of the second half for real? Is Yilber Diaz a starter? And what the heck happened to Jordan Montgomery? This led me to discovering a new pitch I hadn’t ever even heard of before, as well as changed my mind about some of these guys’ long term outlook.
Lets get to the basics first. For the most part, statcast defines breaking balls as either curveballs (red below) or sliders (blue below). There are many variations both, but for the most part you can lump any breaking ball as belonging to one of these 2 families. When looking at the graph below, think of the trajectory of the pitch coming from a right handed pitcher where the lines cross being a perfectly straight pitch with no induced movement.
Curveballs generate a great degree of vertical movement due to topspin. Sliders generate movement based on gyro spin. In recent years sliders and curveballs have been sub divided further into more specific categories. For the purposes of this article, lets focus on sliders.
Most people have probably heard of the sweeper by now as it has quickly become popular in the sport. A sweeper (yellow below) is just a slider with much less vertical movement than a traditional slider. For Dbacks fans, think Brandon Pfaadt. His slider appears to move completely horizontal with almost no vertical drop.
In addition, there is also the slurve. The slurve (green below) is a pitch that borders between a slider and a curveball with both vertical movement and horizontal movement.
Finally there is the Deathball (orange below), or sometimes referred to as the gyro slider, that has very little horizontal movement and almost exclusively vertical movement.
So why do we care and why and the heck is it so important to the Dbacks in 2025? I’ll cut to the chase. In recent years the Deathball has been a breakthrough for pitchers with a high over the top arm angle who struggle to pronate and throw a more traditional 12/6 curveball or have a consistent changeup with arm side movement. The pitch has become popular in recent years with the rise in rhapsodo spin machines and pitching labs. The technical term for the pitch is -2 horizontal to +2 horizontal with 4 inches or more of vertical movement. Upon meta analysis, it was found that pitches inside those movement parameters were swung at and missed almost 50% of the time per Tread Athletics. Naturally with that much success, pitching labs have been all over it. Especially with pitchers with high arm slots that struggle to throw traditional 12/6 curveballs or have consistent command of a changeup or splitter.
Ryne Nelson pre 2024 is a perfect example of this:
The majority of Nelson’s movement profile could be captured in that black circle above. Either Fastballs or breaking pitches that moved away from a right handed hitter. He was very 2 dimensional.
Now let’s look at 2024 Nelson:
Notice how much less horizontal movement Nelson’s slider has and what that does to his pitch movement distribution. The black circle is much more vertical and less horizontal. The further the season went along, the less horizontal movement Nelson’s slider had and the more of a Deathball he was throwing. This gave him much more of a vertical pitch movement arsenal that plays to lefties and righties.
The true power of the deathball is when a pitcher has a high release point like Nelson’s 48 degrees and almost no horizontal movement with vertical drop, the pitch appears to almost run armside like a screwball. This is an especially powerful pitch for a righty against a lefty. And a movement pattern Nelson didn’t have in 2023. Here is an example:
Notice the shape of this pitch (yellow line) and how it almost appears to move in on Teoscar Hernandez. It also has a high degree of vertical movement. If you were watching this pitch and didn’t know any better, it almost moves like a splitter.
In 2024 batters hit just .226 off the deathball slider and in the later months of the season he was throwing it almost 15-20% of the time. At the same time he really started taking off. Post all-star break Ryne Nelson pitched to a 3.23 ERA over 64 innings.
If Nelson’s second half success was due to this tweak to his slider, and he carries into 2025, the Dbacks could have something special. It honestly me a little nervous to move someone like this out of the Dbacks rotation.
So who else on the Dbacks has a high release point and throws the deathball? Here is another Pitch movement profile:
Look at that slider sitting almost in the exact middle with almost pure gyro spin. If you guessed Yilber Diaz, you would be correct. Diaz is another pitcher that throws almost exclusively traditional glove side moving pitches lacking a changeup, splitter, or a sinker. On the surface, this could also be problematic. This is much of the reason why many are less than optimistic about Diaz’s ability to stay in the starting rotation. How is he going to get lefties out without a solid changeup, splitter, or sinker? I used to think like this as well.
However when Diaz got to the bigs, lefties actually struggled against him more than righties did with a .255 BAA vs a .259 BAA in almost identical sample size. Thank you deathball! Because of this, I actually am more bullish on Diaz’s ability to stick in the rotation and he may actually have a much higher ceiling than many will realize. Opposing batters hit just .130 of Yilber Diaz’s deathball in 2024 with an almost 40% whiff rate! Not someone I really want to trade to be honest. Especially with his elite fastball.
Now the ultimate deathballer mentioned in many of the deathball videos: Jordan Montgomery. Now Monty actually throws his much slower than Diaz or Nelson so statcast has been calling it a curveball more often than not, but if we look at the spin as well as the movement profile, it looks much the same:
Of more interest to you all, here is where his deathball was in 2023 when he enjoyed a lot more success:
Notice how much more vertical this pitch was for him in 2023. About 1.3 MPH harder and more vertical with less slurvy horizontal movement.
In 2023, opponents hit .191 against Monty’s deathball. In 2024? .270. In addition it is also possible due to that pitch being less effective, hitters were able to sit on Monty’s usually effective sinker more.
If Monty can rediscover his 2023 deathball? The Dbacks may want to hang onto him. Keep in mind Brian Kaplan’s background is in the driveline pitching lab. He likely knows a thing or 2 about the pitch.
In conclusion, the Dbacks may want to stand pat with these 3 starters as they may have unlocked something in both Nelson and Diaz and they may be able to use Kaplan and his pitching lab experience to renew Monty’s 2023 deathball. If you’ve made it this far, thanks for the read and I’d love to hear your thoughts in the comments!