Have the Rays been targeting a specific slider shape?

The Rays have a reputation for finding pitchers other teams didn’t want and few fans have heard of and then instantly turning them into good major league relievers.

It’s a cliche at this point, fodder for playoff bingo. And while that narrative is likely overblown, it’s worth paying attention to the moves the Rays make on the margins, because that’s where organizational philosophy shows itself most clearly.

The more interesting story is not that these pitchers came from nowhere. It’s that while it may not be immediately obvious, they usually all do something very well.

This article is going to focus specifically on a handful of moves and adjustments the Rays made in the 2021 season. First up are a couple of minor signings:

• May 18th, 2021: Rays acquire RHP Sean Poppen from the Pirates for cash considerations
• July 30th, 2021: Rays acquire RHP Shawn Armstrong from the Orioles for cash considerations
• August 3rd, 2021: Rays sign RHP Evan Phillips to a minor league deal

If you are asking yourself, “Those pitchers were on the Rays in 2021?” that’s completely fair and you probably aren’t alone. Phillips and Poppen only appeared in one game for the Rays last season before being designated for assignment. Armstrong pitched in 11 games before suffering the same fate. None of the three pitchers are still in the organization.

But while they were only short-term moves, the Rays went out of their way to acquire these arms. There are hundreds of pitchers who are placed on waivers and/or signed to minor league deals every year, so why them?

To answer that, lets first look at video on each of them from the 2021 season. It isn’t coincidental that they all have the same primary out-pitch: a slider. And not just any slider, but a very specific shape.

Here’s Armstrong’s slider:

And here’s Phillips’s version:

And finally here’s Poppen’s slider:

After watching those videos, you can see the similarities between the three pitches. All of them are mid-80’s, bat-missing sliders with big sweeping movement. It’s tough to know just how unique these sliders are with respect to the rest of the league just by watching video, though. That’s where the numbers come in.

Baseball Savant has given us easily accessible leaderboards for Statcast metrics and measurements, including pitch movement, and seeing these three pitchers’ sliders in a league context really shows how the pitches are alike.

Velocity is the speed of the pitch in miles per hour, measured shortly after it leaves the pitchers hand. Horizontal movement is the amount the pitch moves side to side in comparison to a theoretical straight pitch. For a slider we’re talking glove-side movement. When these two measurements are used as the axes on a scatter plot, a couple takeaways quickly become noticeable:

First, there is definitely a negative correlation here between velocity and horizontal movement. This makes sense because the pitches that are thrown harder have less time in the air to move compared to slower pitches. For example, the plot shows us that nobody in the league averages a 90mph slider with over 10 inches of horizontal movement, it’s not humanly possible.

The second observation has to do with the three Rays pitchers mentioned before. All of them are highlighted in the plot above and wow, they stand out! They all are on the far end of the horizontal movement spectrum, meaning they get a ton of sweep on their sliders. What’s also interesting is that these sliders are all also thrown quite hard considering the amount of movement they get.

For instance, Evan Phillips gets an average of 15.3 inches of horizontal movement on his slider, that’s high! What is even more impressive is that he is doing it at an average velocity of 84.4mph. In context, you can see how unusual this type of movement-speed combination is. All three of these guys are a good bit above the best-fit trendline on the plot, which speaks to their strong ability to spin a slider.

The Rays are coaching their pitchers to add horizontal movement to their sliders

Not only did Tampa Bay target these high-velo sweeping slider qualities in pitchers from outside of the organization, they worked with pitchers already on the Rays staff to tweak the shape of some existing sliders as well.

The first example of a slider shape change in 2021 comes from Louis Head, who signed a minor league deal with the Rays in February at age 30, and who the Rays just now traded to Miami amid a 40-man roster crunch.

In an interview with David Laurila at FanGraphs, Head said the following:

“It was the information being relayed back to me being told in a way that made sense. From where my arm slot is… my slider was more of an up-and-down curveball shape in the past, and teams were trying to get me to go up-and-down with it to match a fastball that I would ride to the top of the zone. When I got here — this was after two or three bullpens — they were like, ‘No, with your arm slot you need to sweep that slider.’ Getting more horizontal break on it, and less vertical break on it, has really just made a world of difference. It goes off the plane of my fastball better; hitters see fastball out of the hand. When it was more up-and-down, they were able to dive down and get it. Now when they try to dive down to get it, it’s going away from the barrel.”

Very interesting! The Rays made this change with him right away, and it almost feels like they signed him with the specific intention of changing his slider shape.

Before this season, Head spent 8 years in the minor leagues without being able to break through. In his first season with the Rays, he threw 63.2 IP with a 2.26 ERA, 69 strikeouts, and just 19 walks across both Triple-A and MLB. There is no public data on Head’s slider from previous seasons (because he was never called up), but based on his fantastic 2021 results, changing the shape of the pitch seems like a significant adjustment.

Here is a look at that new and improved slider from Louis Head:

Another pitcher who appeared to be tinkering with slider shape this season was hard-throwing righty Drew Rasmussen.

Rasmussen has always had a sharp slider, but he, like Head, used to get most of his movement in the vertical direction rather than horizontal. Well, at the end of the season it looks like Rasmussen tried to adjust that. Check out this chart via Brooks Baseball that plots his average slider horizontal movement in each game he pitched in 2021:

Do you notice a trend here? It is no accident that the horizontal movement ticked up on his slider in his final few appearances this season.

This particular slider in the video below came in his final start of the regular season and induced a swinging strikeout from Yordan Alvarez. It was thrown at 86 mph with nearly 14 inches of horizontal movement, very similar to the numbers that Armstrong, Phillips, and Poppen showed this season.

If Rasmussen can keep that slider shape in 2022, watch out, because the Rays may have just developed a new lethal weapon for an already very promising young arm.

Why is Slider Horizontal Movement Important?

Now that we have identified the type of sliders (above average horizontal movement for their velocity) that the Rays have been after, the next question is why are they after it?

Using Baseball Savant, I pulled the data on every single slider that was hit into play in MLB this year (20,682 results). On the X axis, the sliders are grouped into buckets based on their horizontal movement. So for instance, if a slider was thrown with 9 inches of horizontal break, it is captured in the 8-10 inch bucket.

The Y axis shows the average Hard Hit % (exit velocity over 95 mph) allowed for all of the sliders thrown in each bucket. The overall average Hard Hit % allowed for all sliders thrown this season was 33.6%.

The trend is apparent right away, more horizontal movement means weaker contact allowed. It’s not surprising, but it’s good to see the numbers confirm what common sense suggests. Batters struggle to square up pitches with more break.

For more evidence that the Rays value horizontal movement on breaking balls, look no further than 2 of their free agency signings from just last offseason: Collin McHugh and Rich Hill. McHugh’s slider averaged 18.7 inches of horizontal movement while Hill’s curveball averaged 20.1 inches. Both pitches ranked amongst the league leaders in that metric for their respective pitch types.

Why is Slider Velocity Important?

Using the same methodology, I pulled more slider data from the 2021 MLB season. This sample of sliders however does not just include the ones that were put into play like before, but includes all sliders that resulted in a swing. This way we are able to calculate Whiff%, which is simply the number of swings and misses divided by the total number of swings. The data is broken down into groups just like before, but this time using pitch velocity buckets instead of movement buckets:

Once again we see a clear trend, the harder thrown sliders lead to more swings and misses.

Side note: Intriguingly, while high velocity leads to more swings and misses, and sweeping movement leads to more soft contact, there’s little correlation in the other pairing. That extra movement does not appear to dramatically increase the chances of whiffs, and adding velocity does not appear to help limit hard contact. But remember that speed and movement themselves are inversely correlated with each other — a good reminder that pitching is complicated.

The final conclusion here is that slider horizontal movement creates more soft contact and slider velocity creates more whiffs. A slider with both qualities is a special pitch.