Tuesday, July 23, 2024
AnalysisChicago CubsMLBNational LeagueNL Central

The Upside of Jeremy Jeffress and the Struggles of the Sinker

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Photo Credit: Baseball Savant

On Tuesday, January 28, it was announced that the Cubs bulked up their bullpen with another low-risk signing in Jeremy Jeffress. Jeffress, the familiar former Brewers relief pitcher, was signed to a one-year, $850,000 deal.

This move follows the Cubs’s trend this offseason, signing low-risk and high-reward deals. Jeffress is just one of a myriad of relief pitchers under this archetype, including Dan Winkler, Brandon Morrow, and Ryan Tepera.

The thing that Jeffress boasts more than all of the other ones they have signed is a truly elite relief season. While his extraordinary 2018 season is highly improbable, his upside is still intriguing and has admirable value.


Jeffress has been a valuable relief pitcher in his tenure. Since 2017, he boasts a 3.81 SIERA, 3.84 xFIP (89 xFIP-), 22.7 K%, and 13.2 K-BB% in 819 TBF. While these stats are carried by his 2.87 SIERA, 2.86 xFIP (70 xFIP-), 29.8 K%, and 20.7 K-BB% in 299 TBF in 2018, he was still adequate in 2019. While not elite, he did post a 4.21 SIERA, 4.40 xFIP (99 xFIP-), 20.4 K%, and 12.9 K-BB% in 225 TBF.

Jeffress’s main dilemma is one that has become very common among players. The dilemma lies in one pitch: his sinker.

It’s difficult to dissect exactly why the sinker has been such a struggle for so many pitchers. When comparing it with the two most common fastball types (four-seam and two-seam) since 2017, there is a very similar xwOBA. The sinker is at .358, while the other two are at .351. However, a reason can be concluded using the 2019 juiced ball.

In a spectacular Athletic article by Dr. Meredith Wills, an astrophysicist and sports data scientist, she found that a new baseball was used last season, dubbed the “dragless baseball” in another article dissecting it by Connor Kurcon and Ray Butler. She found that the dragless baseball had fewer factors against air resistance, which Connor and Ray dive into more in their piece, which let the ball travel further.

Given the fact that fewer factors fight against air resistance given this new ball, it reckons to hypothesize that less movement and velocity on a pitch can make it perform worse. Luckily for us, the magic of Baseball Savant concludes this quite swiftly. To measure this, I compared the sinker, four-seam, and two-seam in multiple variables that affect the outcome of the pitch. The reason behind using the four-seam and two-seam was their frequency, given a 36.0 and 8.4 pitch%, respectively.

The sinker’s xwOBA is 9 points higher than for the four-seam and two-seam, at .363 to .354 respectively. In spin rate and average pitch velocity, it lacks behind them by an adequate amount, with the four-seam more significant than the two-seam. It lacks behind the four-seam in each by 150 RPM (2287 to 2137) and 1.2 MPH (93.4 to 92.2), respectively. With the two-seam, it’s less significant, given a difference in RPM of 36 (2173 to 2137) and MPH of 0.5 (92.7 to 92.2) in favor of the two-seam.

There’s a way we can take this one step further, however, using average perceived velocity. Found using the same method, this stat uses the average pitch velocity and release point of the pitcher to show how fast the pitch seems to the hitter. The sinker lacks behind both the four-seam and two-seam in this pitch as well, with a difference in MPH of 1.39 (93.28 to 91.89) for the former and 0.54 (92.43 to 91.89) for the latter.

To illustrate the sinker’s effect on Jeffress himself rather than league-wide, Connor and Ray’s stupendous research must be revisited. They were able to make a stat called “Benefit/BBE%”, which categorized hitters and pitchers by the number of times they hit in the 95-105 mph range and adjusting for different measures of launch angle. In this case, the divisor would be the number of batted ball events by the player. They were also able to adjust wOBAcon, accounting for this difference with delta wOBAcon.

For Jeffress, his Benefit/BBE% signified some poor luck, at 10.20%. In case that was difficult to follow along, that means that over one in 10 of Jeffress’s batted ball events resulted in one of these hard-hit balls to varying launch angles, as they help to weigh the outcome of these events. To take it one step further, Jeffress’s delta wOBAcon (the difference of actual wOBAcon and adjusted wOBAcon ranked above the 60th percentile, at 0.009 (0.373 to 0.364). Essentially, this means that he ran into more poor luck last season than the average pitcher. This isn’t a surprise either, considering that he used his sinker 34.0% of the time.

Jeffress’s sinker has also caused him a lot of trouble beyond 2019. We find his sinker’s wRC+ since 2017 to be approximately 123. However, it trails the mean wRC+ of his four-seam in that same time span by 9. There’s reason to suggest, however, that his sinker may actually be the pitch that’s caused him the most trouble. To start, we can take a look at how he’s thrown his sinker 438 more times, so it’s a more reliable sample, but we can take this one step further. His xwOBA on his sinker since 2017 is .353, which is 29 points higher than the league average .324 since 2017. It’s also 33 points higher than the xwOBA on his fastball (.320). All are calculated using a rough mean method.


Now that we’ve dissected Jeffress’s struggles, the question remains about his role in the organization. As aforementioned, the Cubs haven’t been extremely active in the relief pitcher market, but have gotten enough to guys to formulate a potentially admirable bullpen.

Jeffress could find himself in the running for a set-up role. Some of the Cubs’s high-end bullpen talent runs on the upside of players without pedigree, such as with Brad Wieck and Trevor Megill, so the Cubs may value experience at the beginning of the season. If so, Tepera, Rowan Wick, and Jeffress may be the guys most highly in the running. Out of those three, Jeffress is the only one who’s had one or more sub-3 SIERA seasons, giving him the most initial upside.


This late in the offseason, signings are to add depth to minor needs throughout positions. Jeffress does fill that description, having struggled more in the prior three seasons than his upside would indicate. However, his upside and overall prior dominance span beyond that description and could, potentially, find its way into a large bullpen role for the team for the 2020 season.

SIERA, xFIP(-), K%, K-BB%, TBF, wOBA, and wRC+ are found on FanGraphs.

Pitch%, xwOBA, spin rate, average pitch velocity, average perceived velocity, actual wOBAcon, and xwOBA are found on Baseball Savant.

Benefit/BBE%, actual wOBAcon, adjusted wOBAcon, and delta wOBAcon are found on Connor and Ray’s leaderboard.

Steven Pappas

Hello! My name is Steven Pappas, and I'm a high school junior. I love to analyze and write about baseball data as a huge Chicago Cubs fan and lifelong follower of the sport. I use large databases such as Baseball Savant, basic coding knowledge in RStudio, and my inquisitive mindset to always scour the infinite data available. I really enjoy watching and following basketball and am a Chicago Bulls fan, actively going to their games at the United Center. I love the study of filmmaking, and it's a passion that I've begun to explore as a career opportunity. My favorite works come from the minds of Stanley Kubrick, Yorgos Lanthimos, Alejandro G. Iñárritu, the Coen brothers, and Wes Anderson. As a deft and passionate writer, I use my proficiency to create works from baseball data, for films, and my ideas in the form of short stories and little nuggets. I'm also a libertarian socialist in training and an active Greek Orthodox Christian.