With the 46th pick in the 2023 MLB draft, the Rockies selected Sean Sullivan to the surprise of many. Going into the draft, scouting sources ranked Sullivan across the board but unanimously well beyond the 46th overall spot (the draft doesn’t always operate on a best player available system, but that’s beside the point).
MLB Pipeline ranked Sullivan 123rd, Baseball America ranked him 77th, and Prospects Live ranked him 64th. Those latter two sources ranked him much closer to the 46th pick as a late riser, but it was still a surprising pick.
Then the reports started circulating on Twitter and the fact that Sullivan averaged just over 90 mph on his fastball came to light. How could the Rockies select a pitcher inside the top 50 that averages 90 mph?
This is a dramatic simplification, though still a common opinion on draft night in 2023. It now can serve as quite a complex lesson in drafting and pitching more generally. The draft is an opportunity for teams to take players they believe in and that’s exactly what happened with the Rockies and Sean Sullivan. Almost a year later, that belief looks to be very sound.
Coming off a complete game Maddux performance–that he somehow lost–Sean Sullivan has ridiculous numbers. Across 8 starts (49.1 innings), Sullivan has a 2.37 ERA with 57 strikeouts and just 4 (FOUR?!) walks, computing to a wicked 0.93 WHIP. A guy who throws 90 mph performing like that on a difficult first season assignment to High-A?
You’re a Wizard, Sully
He’s a what?
A wizard. Sean Sullivan is a wizard of pitching. He has a truly unique and ‘unicorn’ set of traits that make his stuff like magic. As mentioned above, he serves as a great lesson in the art of pitching and has laid a foundation for a type of pitcher that the Rockies may find a lot of success developing.
Arm Slot & Vertical Approach Angle
Let’s lay the the groundwork by starting with Sullivan’s slot. It’s no mystery that Sullivan is a sidearmer/very low 3/4 slot guy; it’s the first thing you see when you watch him pitch. Sidearm slots can be very effective as they’re uncommonly seen by hitters and usually lead to an uncomfortable at bat.
Sullivan hides the ball very well to right-handed hitters and is super deceptive, nullifying some of the usual splits pitchers see against opposite hand pitching, while his low slot instills fear in left-handed bats. This is the first building block in making Sullivan as effective as he is.
Arm slot goes beyond just the psyche of hitters. In today’s game, the shape of pitches is under a microscope, it’s no longer just about who throws hard and/or locates their pitches. We simply have the data to analyze pitch shapes and what is typically effective or not.
When it comes to fastballs, the modern trend has been to locate fastballs up in the zone. It gives hitters less time to react to the pitch as their hands need to get around faster and it is a more difficult pitch to see. However, not just any pitcher can throw the fastball up.
In comes vertical approach angle (VAA) which measures the angle a pitch crosses the plate, a stat that has taken up prominence in MLB front offices. Think of the default axis line as a straight line to the plate from where the pitcher releases the ball. VAA can then be measured by plotting the height at which the ball crosses the plate and drawing a line from their release point to the ball.
Here’s a nice image from Baseball Connect to serve as a clarifier. The dashed line is the imaginary straight line from the pitcher’s release point, while the red line is the actual ball path, creating the VAA of the pitch. Since pitches travel down from any non-submarine arm slot, the measures will almost always be negative with lower values equating to a steeper angle and higher values equating to a flatter angle.
In baseball, the term flat has traditionally been used to describe a dull pitch that’s easy to hit. However, in terms of locating a fastball up, a heater with a “flatter” VAA can be one of the most dominant weapons in the game. When I was learning more about some of these pitch metrics, this article from the former Iowa Baseball managers proved very helpful to conceptualize the metric and show the correlation between flat VAAs located at the top of the zone and success.
Conversely, steeper VAAs are typically more effective down in the zone, however, pitches down in the zone are hit harder on average.
The main keys of VAA are arm slot/release height and spin based movement. With fastballs, Induced Vertical Break (IVB) is the main movement metric that dictates VAA as it looks to see how much a pitch breaks upward against the forces of gravity (no normal pitch actually moves upward but the more resistance to gravity, the better). In Sullivan’s case, his IVB is pretty standard and even a little below average, however, his arm slot allows him to throw a very flat fastball.
Introducing VAA was critical here to explain the magic of Sullivan. In essence, Sullivan’s lower slot allows him to generate a flatter VAA, regardless of what his pitch metrics look like because his arm path does not require him to follow through as steeply down.
Extension
The biggest outlier trait in Sullivan’s toolbox is his elite extension towards home plate. The best way to think about extension is how much a pitcher shortens the path from their release point to home plate. The less distance the ball has to travel, the harder a pitch can typically be which deceives a hitter, regardless of the true velocity of a pitch.
In Sullivan’s case, he extends 7 and a quarter feet (about 7’3″) to the plate when throwing his fastball. For reference, few pitchers extend over 7 feet with most pitchers extending between 5 and a half and 6 and a half feet to the plate. That extension is a huge separating factor between Sullivan and the average pitcher and helps to explain why he can be so effective despite averaging just 90.7 mph on his fastball last season.
Next time you see Sullivan sitting 90-92 on the radar gun, remember his top tier extension makes the pitch play roughly 2-3 mph faster and we all know mid-90s velocity will play.
The combination of Sullivan’s arm slot and extension make him one of the most unexpectedly difficult at bats for hitters as there are so many factors their eyes need to adjust for. Over time and with more extensive scouting reports, hitters will get more comfortable, but it’s still hitting–arguably the most difficult skill in any professional sport–and any amount of preparation doesn’t all of a sudden make things easy.
Sullivan is one of the most unique pitchers in professional baseball and will continue to be a difficult task for hitters for a long time, as a result.
Precision
Sullivan’s arm slot and extension are two of the most important parts of his game. However, they’re both controlled pre-release. Sullivan wouldn’t be a great pitcher if that was all he had in his bag of tricks.
Fortunately, Sullivan is also a master of command. Because Sullivan isn’t a hard thrower, he’s able to use more controlled mechanics and has been dominant throwing strikes and locating in ideal zones. His walk rate speaks for itself.
However, Sullivan also has a knack for living away from hitters. Like locating up with a metrically friendly fastball, locating away from hitters is a prime way to avoid damage. You never want a pitch to break towards a barrel in the strike zone, otherwise, that ball may go a long way. So Sullivan uses his changeup–primarily to righties–and his slider–primarily to lefties–to keep hitters from getting their barrel to the baseball (a very similar attack plan to fellow Rockies lefty Carson Palmquist).
The Pure Stuff
So Sullivan must be making up for the fact that his stuff is only average right? Nope. Sullivan is no Pedro Martinez but his pitches all have above average movement.
Starting with his heater, Sullivan gets above-average armside run, largely because his arm slot requires him to release the pitch more horizontally, getting on the side of the baseball. His fastball doesn’t get a ton of carry-up in the zone (would be the product of getting underneath the baseball) but he doesn’t need to because of his arm slot.
Sullivan’s changeup gets above-average horizontal movement, for the same reasons his fastball does. This allows the pitch to very effectively work away from righties. Sullivan’s changeup is his third pitch and not quite a standout offering, though it is certainly an average (50 grade) or better piece of his arsenal.
In terms of his slider, this is where Sullivan puts himself over the top. Sullivan’s pitch gets above-average movement on both planes. It sweeps across the zone and has plenty of depth to drop down in the zone. This time of movement profile makes it borderline unfair for left-handed hitters to try and match.
Connecting the Dots
To connect the dots here, Sullivan has nearly every pitcher trait working in his favor, except pure velocity. However, he makes up for it with his elite extension, his arm slot allows him to throw a devastating elevated fastball, his changeup and slider are both effective, and he’s as precise as can be. While Sullivan doesn’t have a deep arsenal, the pieces are all here for him to become an effective backend starter in short time.
Connecting the dots with the Rockies organization at large, expect them to target pitchers like Sullivan more often. We all know Coors Field isn’t friendly to pitch movement and finding characteristics in pitchers that are immune to altitude–think arm slot and extension which impact a pitch before it’s released–will be very key. The Rockies may benefit more from extreme arm slots than other organizations as they try to mitigate the impacts of Coors Field as much as possible.
Think of Sullivan as a new blueprint for pitching success at Coors Field, though the Rockies aren’t going to be able to find anyone quite like him, they simply need to keep targeting unique arm slots and pitchers that extend well towards the plate. Sullivan’s combination of outlier traits make him pitch like a true wizard of the sport.
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