The Diamondbacks' Bullpen is Better Than Their ERA. Here's Why

A deep dive into the numbers is quite telling.

Aug 23, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Brandyn Garcia (55) throws against the Cincinnati Reds in the ninth inning at Chase Field. Mandatory Credit: Rick Scuteri-Imagn Images | IMAGN IMAGES via Reuters Connect

The Arizona Diamondbacks are coming off an impressive performance by their bullpen. Seven pitchers combined to throw nine shutout innings in a 1-0 victory over the Philadelphia Phillies on Wedneday, September 3.

This was just the latest chapter in a story that has been developing all season for the D-backs. All season long fans and pundits alike have heaped praise on the Diamondbacks relief corps. A cursory look at the team's 4.10 bullpen ERA doesn't show anything special. That ranks 17th in MLB and eighth in the National League.

But that one metric falls far short of of explaining the value of the 2026 bullpen. It's been a cornerstone of their success in a season where they currently sit in the third NL Wild Card spot with a 74-67 record, a half game in front of the San Diego Padres.

Why The Diamondbacks Bullpen is Better than Their Raw ERA

Diamondbacks vs MLB Avg Reliever ERA by Leverage | Jack Sommers

In a word: leverage. The Diamondbacks' core group of relievers have performed exceptionally well when it's mattered most, in high- and medium-leverage situations. In fact they rank 4th-best in MLB in those situations.

The inflated number showing in low-leverage situations in the table above is due to position players and an assortment of low-leverage relievers giving up runs when a game is lopsided, in either direction. Those low-leverage runs allowed tend to obscure the excellence of the bullpen as a whole.

Another metric that illustrates this point is WPA, or Win Percentage Added. That is a metric that looks at the win expectancy before and after each at-bat, and either credits or debits the pitcher (and the hitter) the difference.

The Diamondbacks' +6.33 WPA ranks 4th best in all of MLB, behind only Atlanta Braves (10.49), Milwaukee Brewers (7.60) and Tampa Bay Rays (7.12). That is rarified air for an organization that has typically struggled to put a good bullpen on the field in most seasons.

Bullpen Depth is the Key for Manager Torey Lovullo

D-backs Relievers in High and Medium Leverage Situations, Ranked by ERA | Jack Sommers

In years past, the Diamondbacks might have had two or three "positive-role" relievers, a term Lovullo uses to describe high-leverage relievers. Beyond that, he typically had four or five pitchers that would slot in behind them.

But the situation is different now.

"For the first time in quite a while, I feel like there's a lot of guys that can step up," Lovullo said.

The table above illustrates this point. There are eight relievers who have faced at least 20 batters in high or medium leverage situations. All but one — former closer Paul Sewald, now aToronto Blue Jay — have an ERA at least one full run better than the league average 4.70.

Gerardo Carillo has the smallest sample, and he's struggled a bit with command lately, but it's notable that he's contributed in this way in high leverage. Taylor Clarke, Juan Morillo, and Brandyn Garcia have been outstanding. Jonathan Loaisiga and Kevin Ginkel have been much better than average on the season as well, despite a few hiccups from Ginkel this past month.

Even Ryan Thompson, who is on the 60-day injured list with a back injury and lost for the year, performed nearly two runs better than league average in high and medium leverage.

Summary

Aug 28, 2026; San Francisco, California, USA; Arizona Diamondbacks catcher James McCann (8) and Arizona Diamondbacks pitcher Juan Morillo (62) celebrate after defeating the San Francisco Giants at Oracle Park. Mandatory Credit: Stan Szeto-Imagn Images | IMAGN IMAGES via Reuters Connect

The Diamondbacks have a 24-19 record in one run games. They play a lot of them, as their total of 43 such contests is among the most in the league. They have a league-average offense at best; that has been inconsistent of late.

There have been numerous injuries to the rotation, and they'll be depending on returning injured starters who are trying to up their pitch counts over the final three weeks of the regular season.

The bullpen is going to have to continue to carry a heavy load and perform well in tight situations for the D-backs to get to where they want to go and capture a Wild Card spot.