The Arizona Diamondbacks Bullpen Has Been Tops in the NL in September

Ryan Thompson, a key addition to the Diamondbacks bullpen, the best in the NL for the month of September so far.
(Photo by Chris Coduto/Getty Images)

Arizona Diamondbacks: The NL’s Best Bullpen in September

For several years, the Arizona Diamondbacks’ most glaring weakness has been relief pitching. While improved in 2023, they still were in the bottom ten in the majors and bottom five in the NL for most of the season. September, however, has been a different story, as the Diamondbacks have the highest-rated relief corps in the National League for the month. In addition, they are 0.1 points behind the Detroit Tigers for the top ‘pen in the majors.

Overall leaderboards for September, through end of play Sept 14. AL (red) on the left; NL (blue) on the right.

Performance in September

Diamondbacks relievers have put up zeroes in September at a higher rate than any other team in the NL. In 45 relief appearances by players in a Diamondback uniform (excluding position pitching), they have allowed an earned run eight times. This gives them a scoreless outing percentage (earned runs only) of 82.2%, the best rate in the National League. In the American League, only the Tampa Bay Rays (92.3%) have a higher rate. For context, the NL average is 71.6% and AL average is 71.4%.

Individual numbers are also impressive. So far in September, 11 pitchers have made at least one relief appearance for the Diamondbacks. Five have 100% scoreless outings — Andrew Saalfrank (4-for-4); Bryce Jarvis (2-for-2), who was optioned to Reno September 7; Luis Frias (5-for-5); Miguel Castro (5-for-5); and Ryan Thompson (4-for-4). Joe Mantiply, Kevin Ginkel, and Paul Sewald are all at 80%, 4-for-5 when counting earned runs only. Kyle Nelson is at 75% (3-for-4). The remaining two are Scott McGough (2-for-5, 40%) and Brandon Pfaadt, a starter who allowed runs in a piggyback role, his lone relief appearance.


Clutch has also been a strength in September despite being a glaring weakness for the rest of the season. Sport Relay uses Goose Eggs and Broken Eggs in lieu of saves and blown saves (reasoning and stat explanation here). The Diamondbacks have seven Goose Eggs and no Broken Eggs in September. In other words, from the seventh inning onward in tie games or while holding a lead of no more than two runs, the Diamondbacks have pitched in eight innings. They did not give up an earned run in any of them, and in seven, they didn’t give up a run at all. (The eighth saw the automatic runner score but no one else.)

Under these conditions, Ginkel, Sewald, and Thompson have pitched two scoreless innings each. Saalfrank pitched the seventh scoreless inning.

Other Stats

The Diamondbacks are third in the NL in September for reliever WHIP with 1.061, 216 points below the league average of 1.277. Only the Los Angeles Dodgers (0.969) and Pittsburgh Pirates (1.023) have a lower reliever WHIP in the month. Five Diamondbacks have WHIPs below 1.000 — Thompson (0.214); Frias (0.400); Castro (0.643); Ginkel and Saalfrank (0.750 each).

The final category Sport Relay uses in its reliever rankings — and the one with the lowest weight — is command, which uses strikeout percentage minus walk percentage (K-BB%). As a team, the Diamondbacks are sixth in the NL out of fifteen teams (14.4%; NL average is 13.6%). Individually, however, there are four Diamondback relievers with 20.0% or higher — Ginkel (42.1%), Castro (33.3%), Frias (21.1%), and Saalfrank (20.0%).

Factors in the Strong Diamondbacks Bullpen Performance

Right-hander Scott McGough attributes the overall success of the unit to “tightening the screws up” and everyone having “solidified roles.” Manager Torey Lovullo said, “It’s been a handoff mentality. We have some guys that have carried us early in the year that have handed it off to some newer blood. The injection of Ryan Thompson and Andrew Saalfrank has certainly helped us. We’ve had some guys that have had some very consistent years. And then getting Paul Sewald really was something that made us it solidify things for us.”

Lovullo continued, “It’s kind of been a cycle. Early on, the bullpen was extremely hot and carrying the workload. They hit a little bit of a lull, (and) the hitters took off. The bullpen handled another little bit of a lull. We got some reinforcements, and that’s where we are today.”

The Reinforcements

The “reinforcements” are the three newcomers — Sewald, Thompson, and Saalfrank. This trio has helped the relief unit out, not only with their performance but by giving Lovullo a higher number of trustworthy options. Lovullo said Sewald gave him a “legitimate ninth-inning closer” and added that he can “build in front of that.” Left-hander Kyle Nelson added, “He’s got a ton of experience — fresh experience in the playoffs,” referring to Sewald’s experience in the 2022 postseason with the Seattle Mariners. In addition, according to Nelson, Sewald is “a joy to be around.”

Thompson, who came to the Diamondbacks in August after spending three and a half seasons with the Rays, has a “quirky angle” in his delivery and brings “the energy of someone who’s seen things, especially playoff games,” according to Nelson, who added that Thompson pitched in the 2020 World Series. He is someone who can “come in and go about his business the right way,” according to McGough. Lovullo noted Thompson’s “ability to pound the zone” to get both early outs and weak-contact outs.

Saalfrank, a lefty, was called up September 4 and made his big league debut the next day against the Colorado Rockies. He has fit in well with the team, asking questions and soaking up the knowledge. McGough said he’s “done such a good job as a rookie coming up, looking at what everyone’s doing, and blends in really well.” Nelson pointed out that he tries to “sponge a lot of information,” something that is the “best thing to do” when first coming up. “Listen as much as you can,” Nelson said. While on the mound, Saalfrank “attacks you,” in the words of McGough. “He’s not scared. He attacks.” Saalfrank does so with “swing and miss stuff,” according to both Nelson and Lovullo.

Looking Ahead

Having the best-performing relief unit in the NL over the month of September has kept the Diamondbacks in the playoff hunt. The three newcomers have been a big part of it, not only with their own performance but with what they’ve contributed to their teammates. “I’ve watched their personalities morph and grow as they’ve become more comfortable each day,” Nelson smiled. “It’s been really nice,” adding that it’s something that’s necessary to have a “good, functioning bullpen unit.”

Category Breakdowns

Team-by-team scores in the Clutch category.
Run Prevention scores, team by team
Baserunner Prevention scores, team by team
Command scores, team by team

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Evan M. Thompson, Editor-in-chief

Evan M. Thompson, Editor-in-chief

Evan is the owner and sole contributor of Thompson Talks, a website discussing the Big Four North American Pro Sports as well as soccer. He also is a credentialed member of the Colorado Rockies press corps. His first and biggest love is baseball.

Evan lives in Gilbert, Arizona and loves history, especially of sports. He is the treasurer for the Hemond Chapter of the Society for American Baseball Research (SABR) and also is a USSF and AIA soccer referee. He released his first book, Volume I of A Complete History of the Major League Baseball Playoffs, in October of 2021.

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