Jordan Weems was a third round draft pick of the Red Sox in 2011. Weems, who the Sox signed away from a commitment to Georgia State, was drafted as a catcher, and played behind the plate for the first five years of his professional career. However, in 2016, the Red Sox converted Weems to a relief pitching role. He slowly rose through Boston’s minor league ranks before signing a minor league contract with the Athletics before the 2020 season, where he eventually broke through into the majors. However, Weems has always been a fringe player in the Major Leagues. In his time with the A’s, Diamondbacks, and Nationals, Weems has floated between the MLB and AAA ball, providing inconsistent results when he is up at the MLB level. This year, though, Weems has had a very solid season since being promoted from AAA Rochester at the beginning of June. He’s pitched to a 2.19 ERA with a .119 opponent batting average, adding much-needed stability to a struggling Washington bullpen. So, what’s changed for Jordan?

I started thinking about Weems’ success this year during yesterday’s game, when he gave up a solo home run to Ha-seong Kim in the 7th inning. This home run did not have any impact on the end result of the game — Kim’s solo shot narrowed the Nats’ lead to 8–2, and the Nats went on to win the game 8–3. In a 2–2 count, Weems threw a completely uncompetitive pitch, and the Padres’ shortstop took advantage of Weems’ mistake. 

Ha-Seong Kim’s solo homer (8) | 06/25/2023
Ha-Seong Kim drives a solo home run to left field to get the Padres within six runs in the bottom of the 7th inningwww.mlb.com

This was the third home run Weems allowed this year. Perhaps unsurprisingly, there’s a similarity among all three pitches that opposing hitters took Weems deep on: all three pitches were fastballs. Weems touts one of the highest-velocity fastballs on the team, with only Hunter Harvey and Kyle Finnegan sporting a higher fastball velocity average. It’s also his least effective pitch. Opponents are slugging a shocking .929 against the pitch, a trend which has existed for Weems’ entire career. He is known for his fastball, and he has a powerful fastball, but it’s simply not a quality pitch. 

Here’s the part of the blog post where I do something a little controversial: praise the Nationals’ coaching staff. Weems has had such a drastic turnaround this season because he has stopped relying on his fastball. Instead, Weems has become a slider-first pitcher. His slider has consistently been a secondary pitch; in his rookie season with Oakland in 2020, Weems threw the slider just 18.5% of the time, while he threw the fastball over 60% of the time. In 2020, opponents hit .296 against the fastball but just .083 against the slider. This year, however, he has only thrown his fastball 44.3% of the time, while turning to the slider 48.9% of the time, and the results have been revolutionary for Weems and the Nationals. Jordan Weems has not given up a single hit on any of the 86 sliders he has thrown this year, good for a 35.7% put-away % (35.7% of sliders Weems throws in a two-strike count end in a strikeout). Weems’ fastball has a put-away % of 6.7%, down from 13.6% last year. The improvement lies within the pitch itself, too; last year with the Nationals, Weems’ slider had a 17.5% put-away %. In the video below, you can see a disgusting slider Weems used to strike out Paul DeJong in the Nats’ recent series against the Cardinals. 

Paul DeJong strikes out swinging. | 06/19/2023
Paul DeJong strikes out swinging.www.mlb.com

Weems has made an adjustment to his pitch mix throughout the season, working with his catchers and coaches to make his best pitches in a situation. You can see this adjustment in Weems’ first appearance with the Nationals this year, an inning of relief against the Diamondbacks on June 7. Against first two batters Weems faced, the righty threw four fastballs and one changeup. In that sequence, he gave up a single to Ketel Marte and a two-run home run to Corbin Carroll, one which extended Arizona’s lead outside of the parameters of a save situation. 

For the remainder of the inning after Carroll’s home run, Weems threw eight sliders and three fastballs. He induced three flyouts against Emmanuel Rivera, Christian Walker, and Evan Longoria, ending the inning unscathed.

Sometime between the end of the 2022 season and Weems’ debut in early June, a Nationals coach realized the discrepancy between the success of Weems’ fastball and his secondary pitches. Whether this was noticed by Nationals pitching coach Jim Hickey, Rochester pitching coach Rafael Chaves, or any coach in the organization, this is an analytic victory for the Nationals. Without jinxing Weems’ season, this revelation from the coaching staff has given the Nationals a solid reliever who they could either turn to in a close game or use to avoid overusing their proven “A” bullpen in blowouts.

Many of the Nats’ relievers have similar advanced stat profiles to Weems. This includes former Nat Andrés Machado, who has a nearly analytically identical fastball to Weems. Machado was designated for assignment earlier this season, his failure to capitalize on his secondary pitches leading to his release. For most pitchers, the lack of a solid fastball can derail the trajectory of their career; for all we know, this month could have been a complete fluke from Weems, and he might go on to replicate his form from previous years. It’s important to recognize what is wrong with his fastball and what other Nats relievers should work on to improve their own fastball.

The answer lies in fastball spin rate. Weems’ fastball velocity is in the 88th percentile of major league pitchers, while Machado falls in the 90th percentile. Both pitchers comfortably sit in the mid-to-upper 90s, with both having flirted with 98 and 99 mph on the radar gun. Conversely, Weems is in the 13th percentile of fastball spin rate, while Machado is in the 17th percentile. The concept of spin rate is confusing (here’s a good explainer from Bless You Boys), but essentially, a higher spin rate coupled with high velocity makes a pitch very challenging to hit. The article has a GIF of a Koji Uehara pitch, in which an 88 mph fastball looks nearly impossible to hit due to immense movement from spin. There is a positive correlation between the spin necessary and the velocity necessary to make a pitch that much more challenging to hit. Essentially, Weems and Machado are able to throw hard, but their fastballs do not have the spin to make the pitch competitive against a solid MLB hitter. Weems’ average fastball has 2099 rotations per minute of spin, which is only 7.4% effective at missing bats at 96 mph, per the Bless You Boys article. If Weems were to up his spin rate to 2200, the fastball would instantly become 1.1% more effective at inducing whiffs. Take Tanner Scott, an analytics darling who is having a very solid season out of the Marlins’ bullpen. Scott is in the 86th percentile of fastball velocity – lower than both Weems and Machado – but in the 98th percentile for spin rate. The Marlins’ lefty has an average spin rate of 2600 on his fastball, with the Bless You Boys article calculating that this would lead to an eye-popping 11.3% whiff rate. Scott’s effectiveness stems from his underlying numbers – opponents are just slugging .315 against Scott’s fastball (remember, opponents slug .929 against Weems’ fastball).

There are many ways to increase spin rate, the most notorious of which being the so-called “sticky stuff” that MLB had to begin cracking down on in 2021. The Nats could introduce different fastball grips to Weems, Machado (who remains in the organization, at AAA Rochester), and the team’s other relievers, as only Carl Edwards Jr. is in the top 50% in spin. Edwards is a particularly good mentor for spin rate to pitchers who don’t throw very hard, as he is in the 97th percentile for spin. On a macro level, however, this must be an ideological change in the organization’s pitching philosophy. If the Nats are committed to winning in the long-term, they must cultivate a pitching staff that is analytically forward and make analytically smart free agent signings.

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