The Rays signed Aaron Slegers again. Why?

The interesting pitch characteristics of the 6’10” righty

During the shortened 2020 season, twelve different Rays pitchers threw 20 or more innings, including front-line starters Tyler Glasnow, Charlie Morton, and Blake Snell. Do you know which of those twelve guys had the lowest Fielding Independent Pitching (FIP)? If you read the title of this article you probably have a pretty good guess; the answer is Aaron Slegers.

Slegers has had an eventful first tenure with Tampa Bay, at least as far as his transaction log was concerned:

• 3/30/19: Pirates traded Aaron Slegers to the Rays for cash considerations
• 5/16/19: Rays designated Aaron Slegers for assignment
• 8/21/19: Rays selected the contract of Aaron Slegers
• 9/2/19: Rays designated Aaron Slegers for assignment
• 10/1/19: Aaron Slegers elected free agency
• 1/13/20: Rays signed Aaron Slegers to a minor league deal
• 8/12/20: Rays selected Aaron Slegers to the active roster
• 2/8/21: Rays traded Aaron Slegers to the Angels for cash considerations
• 8/28/21: Angels outrighted Aaron Slegers to AAA
• 8/29/21: Aaron Slegers elected free agency
• 8/31/21: Rays signed Aaron Slegers to a minor league deal

While Slegers did not actually pitch for the big league Rays in 2021, he did get a few outings with AAA Durham at the end of the season.

His value to the Rays major league team came during the 2020 season where he threw to a 3.46 ERA and 3.04 FIP across 26 innings. He also was able to produce great marks in a few Statcast metrics including a 95th percentile chase rate and a 92nd percentile hard-hit rate. No matter which way you slice it, Aaron Slegers was an important arm to the 2020 Rays.

At the beginning of the following year Slegers was then traded to the Angels mostly due to a roster crunch. After Slegers was traded to Los Angeles, he recorded an unimpressive 6.97 ERA and 5.62 FIP. It was a Dr. Jekyll performance when compared to 2020’s Mr. Hyde.

Slegers was outrighted off of the Angels roster in August and the Rays then signed him to a minor league deal the very next day. That tells me that Tampa Bay still sees something they like in the right-hander so I went looking for what that might be.

Unique Sinker Shape

The sinker has always been Slegers’ primary offering no matter which team he’s pitched for. In 2020 it was extremely effective for him as batters hit to just a .135 AVG and a .135 SLG against it — meaning that out of 151 sinkers put in play against Slegers, none went for extra-base hits.

It was a very different story for the pitch in 2021, but Slegers’ sinker still has a very unique movement profile. Check out the graph below, with data from Baseball Savant collected by Alex Chamberlain, which plots release height on the X axis and vertical movement on the y axis:

This plot tells us that, generally speaking, sinkers thrown from higher release points do not drop as much as those thrown from lower release points. This is shown by the positive correlation between the two variables.

The reason for this is that most pitchers with high release points arrive at there through over-the-top release mechanics. This specific release tends to create more backspin, which leads to fastball rise.

Slegers, as you can see in the image below, is getting that release height in part by simply being tall — a full 6’10” — and not by coming straight over the top. This is a part of how he’s able to create so much sink from such a high release point.

Slegers’ high release point mixed with above average drop on his sinker is an uncommon combination. These characteristics create a pitch that comes in on hitters at an extremely steep angle, meaning that the ball is literally moving downward, in relation to the ground, more than most other sinkers.

This concept is known as the Vertical Approach Angle (VAA), which Rays Triple-A pitcher Tyler Zombro does a great job explaining in the video below:

While that video is largely focused on flat approach angles that are important for four-seam fastballs, the other end of the spectrum is where Slegers’ sinker lies.

The extremely steep angle that he is able to get basically creates a pitch that drops more than a hitter is expecting it too. If you want to see what I’m talking about, check out the drop on this strikeout pitch from Slegers in the clip below:

Slegers has always had great drop and a steep approach angle on his sinker, but he hasn’t always had success with the pitch. His sinker was excellent with the Rays in 2020 and I believe that is because another factor is at play here: horizontal movement.

The Rays have recently been loading up on pitchers who possess sinkers with strong horizontal movement and Slegers is yet another example.

Looking back at the shape of Slegers’ sinkers in past years, I found that he was able to get more run on his sinker while in a Rays uniform (2020) than he has in any other big league season:

Horizontal movement was likely a contributing factor to why Slegers’ sinker performed the best of his career in 2020. Time will tell if Slegers is able to get that good run on his sinker again in 2022.

Excellent Sinker Command

A general goal for sinkers is to run the pitch in and under the barrel of a same-handed hitter’s bat, which should help create weak contact and/or ground balls. That can be done by throwing a sinker with strong pitch movement qualities or by placing the pitch in great spots. Slegers actually does both well.

We already touched on the movement aspect of the pitch, now it’s time to dig into how he commands it. First, let’s take a look at the heatmap of his sinker locations in 2020 while he was with the Rays:

This visual is from the perspective of the hitter, and — wow — Slegers was able to live right on that down-and-in corner to righties. If we go a step further, we can quantify his sinker locations in comparison to the rest of the pitchers in the league.

Using Baseball Savant’s search feature, I pulled a list of pitchers who are throwing inside to hitters most often. This table includes pitchers who threw a minimum of 300 sinkers to right-handed batters over the past two seasons combined. Slegers ranks among the elite arms in this skill:

Slegers falls right in the mix with some really impressive names here. Corbin Burnes won the NL Cy Young award in 2021 and both Zack Wheeler and Brandon Woodruff received votes for the award. Locating sinkers inside to same-sided hitters is a very effective way to pitch in this league.

If you’re wondering how this actually looks when Slegers attacks hitters, take this three pitch sequence to Andrew McCutchen for example. The Rays know how strong of a weapon Slegers’ sinker can be and in this match-up they went right after the hitter three times in a row. The first pitch:

Slegers tried to play to his strengths and attack the hitter inside but missed his spot a bit. Rather than mixing things up, Zunino comes right back to the same spot and calls an identical pitch:

Bang. Slegers nails the corner and the count is now even at 1-1. You may think now would be a good time to mix in another pitch to deceive the hitter right? Wrong. The team knows how good that pitch is and Zunino goes back to the well for a third straight time:

Slegers does miss up a bit, but he still got the pitch in enough to get McCutchen to roll over into a double play, exactly as Slegers and Zunino intended. This at-bat is a great example of how a pitcher can be successful by heavily leaning on their strengths, and for Slegers that is his great sinker.

Conclusion

Despite all of the interesting qualities about Sleger’s sinker, the Rays don’t appear to think that it is an effective pitch versus left-handed batters. In 2020, his sinker was his least used pitch against lefties (11.6%) but his most used pitch against righties (55.6%).

Slegers also throws a slider, four-seam fastball, and changeup in addition to his sinker. The other pitches are serviceable, with the slider especially also benefiting from how Slegers’ height creates an unusual vertical angle of approach on the pitch.

It seems likely he’ll start the season with Triple-A Durham, given roster constraints, but with the way that Tampa Bay uses its full roster he’s likely to get a big league opportunity eventually if he’s throwing well. The question remains regarding what length of role, as his most obvious strengths are the ability to pound righties inside with his sinker, but he has the ability to pitch more than one inning of relief as well.

That’s a similar set of strengths to those of Chris Mazza, another righty with an unusual sinker shape who also just re-signed with the Rays on a minor league deal, so Slegers may not even be the first pitcher of his type to get the call when a major league position becomes available, but it’s clear that the Rays like him and think he has talent. It will be fascinating to see what he’s able to do with it in 2022.