What Went Wrong with the Diamondbacks' Pitching?

A deep dive into all the factors that contributed to a pitching staff that likely kept the Diamondbacks out of the playoffs.

Arizona Diamondbacks pitcher Eduardo Rodriguez (57) talks to pitching coach Brent Strom against the Los Angeles Dodgers in the fourth inning at Chase Field in Phoenix on Monday, Sept. 2, 2024. / Rob Schumacher/The Republic / USA TODAY NETWORK

Despite an 89-73 record, the Arizona Diamondbacks fell painfully short of reaching the Postseason in 2024. In fact they missed going to the playoffs by just one game, getting eliminated during a doubleheader between the Mets and Braves one day after their schedule had been completed.

The D-backs scored more runs than any team in MLB (5.47 per game). The team OPS of .777 ranked second in the league, and they led the league in batting average and OBP (.263 and .336).

But as good as the offense was, the team's run prevention was on the complete opposite end of the spectrum. Arizona allowed 4.86 runs per game, ranking 26th in a league that averaged 4.39 runs per game. The Diamondbacks' ERA was 4.62, ranking 27th. They managed to allow more earned runs than the 121 loss Chicago White Sox (741 to 738).

It should have come as little surprise then that the team would miss the playoffs.

In fact, I pointed this out back on September 4. I wrote an article titled "Can Diamondbacks Hang On to Make Postseason With 92 ERA+?"

ERA+ takes ERA and adjusts for the league average as well as ballpark factors. 100 = league average. The higher the better. This allows us to view ERA in the context of league run scoring.

Only three teams in history made the Postseason with an ERA+ 91 or lower, and two of those came in the strike-shortened 1981 season. The three teams to do it previously were the 1913 Philadelphia Athletics, the 1981 Philadelphia Phillies, and the 1981 Milwaukee Brewers. Report Link. Even in this Wild Card era, it hasn't happened yet.

All of this culminated in the Diamondbacks relieving pitching coach Brent Strom, along with assistant Dan Carlson and bullpen coach Mike Fetters of their duties. Strom reacted to the news by taking responsibility, stating "Heavy is the head that wears the crown, and when it comes to the pitching, that's me."

What Went Wrong?

Rotation Injuries

The D-backs put together what looked like a strong rotation during the offseason. They signed veteran left-hander Eduardo Rodriguez to slot in behind Zac Gallen and Merrill Kelly and ahead of Brandon Pfaadt. Then just as the season got underway they signed Jordan Montgomery to join the rotation as well.

Rodriguez suffered a shoulder injury in spring, and ended up missing four months, not returning until early August. Kelly got off to a good start, but after four outings, he too had a shoulder injury, and didn't return until August either.

It's very tough to to come back from a shoulder injury within the same season and be effective. In 10 starts Rodriguez posted a 5.04 ERA, and and a 4.57 FIP. Kelly was no better upon returning. In nine post injury starts he had a 4.96 ERA and 4.49 FIP.

Gallen spent a month on the injured list with a hamstring strain. When he went on the injured list at the end of May he had a 3.12 ERA and 3.27 FIP. He returned June 29 and pitched six shutout innings lower his ERA to 2.83. He was mediocre for most of the remainder of the season however, posting a 4.16 ERA over his final 16 starts.

Montgomery also missed a month with a knee injury, from late June to late July. Whether that contributed to his awful performance, both before and after the IL stint is unknown. He had a 6.44 ERA when he went on the IL, and a 5.96 after he came off it.

Bullpen Injuries

Closer Paul Sewald suffered an oblique strain late in spring training and did not make his season debut until May 7. In his absence Kevin Ginkel converted five of seven saves, but with the relievers pitching in unfamiliar roles, the bullpen suffered.

Left-hander Kyle Nelson got off to a good start, not allowing a run in his first eight games. But something was clearly wrong in his final three outings as his velocity dipped and his command left him. He ended up on the injured list and shortly after it was announced he needed Thoracic Outlet Surgery. Nelson was gone for the season.

Results versus Expected and Peripheral Stats

All teams have injuries and the D-backs had more than their fair share. But the problems extended well beyond the injuries. As a team, the Diamondbacks severely underperformed their peripheral and expected metrics.

Fielding Independent Pitching, or FIP, and it's companion xFIP, are two metrics that derive an ERA equivalent based on the things most under the pitcher's control, which are walks, strikeouts and home runs.

There was a yawning gap between the team's ERA and FIP and xFIP. That gap was higher than any team in MLB, except the Colorado Rockies. Report link from FanGraphs HERE. When broken out by starters and relievers, the gap was considerably higher for starting pitchers. SIERA is Skill Interactive ERA, which takes into account the quality and type of balls in play a pitcher allows.

D-backs ERA vs. Expected ERA / Jack Sommers

BABIP is Batting Average on Balls in Play. To a large degree (but not totally), pitchers have limited control over the ball once it's put in play. Typically when a team has an unusually high BABIP it results in the types of numbers we see above. The Diamondbacks indeed had a .309 BABIP, while the league average was just .289.

Oftentimes teams with a high BABIP against have a below-average team defense rating. But that was not the case with the D-backs. While not quite up to previous year's standards, the D-backs defense was still above average, recording +14 Defensive Runs Saved (DRS) from Fielding Bible, and +21 Fielding Run Value (FRV) from Statcast.

Quality of Contact and Sequencing

The quality of contact the D-backs pitching staff allowed was worse than the league average, but not quite so bad as to explain the large gap between the peripherals and the ERA. Note especially the starters. Their ranks in hard-hit and barrel rates are significantly better than their ERA rank of 27th. That said, these are still worse than average rates for the Diamondbacks' staff.

D-backs Hard Hit and Barrel Rates / Jack Sommers

Oftentimes we heard on the broadcast the lament about leaving pitches in the heart of the strike zone. Using the search tool at Statcast, we can actually check that. The "attack zones" are broken out into heart, shadow, chase, and waste as per the image below.

Statcast Attack Zones / Baseball Savant

The first thing to know is the D-backs didn't actually leave pitches in the heart of the zone more than the average pitching staff. In fact, the opposite is true. Their 26% rate of heart of zone pitches was the fifth-lowest percentage in MLB, compared to a league average 26.6%. Report Link

But when they did so, the results were among the worst in the league. Their batting average against was .332 and slugging was .597. League average is .309 and .545.

The D-backs' numbers were the second-worst in the league, with only the Rockies playing at 5000 feet elevation putting up worse numbers in the heart of the zone. And it wasn't bad luck either, as the xBA was .331 and xSlug was .596.

Furthermore, the hard-hit rate in the heart of the zone against the D-backs ranked 30th with a worst in MLB rate of 51.9%. The 10.4% Barrel rate ranked 26th. But when compared to pitches not in the heart of the zone, their ranks improved to 24th on hard-hit and 16th on Barrel.

The conclusion here is simply that the Diamondbacks' pitchers did not have good enough stuff to get away with pitches in the middle of the zone. When they did so, they got hit harder than almost any team in the league. Brent Strom often said the pitchers needed to vacate the zone more, especially when ahead in the count.

Finally, to see a list of Diamondbacks pitchers ranked from best to worst by wOBA on pitches in the heart of the zone, see THIS LINK. wOBA is the total value of all hits allowed and best combines batting average and slugging against. League average on heart-of-zone pitches is .359, for reference.

Among relievers, it should come as no surprise that Justin Martinez (.270) ranked the best. Surprisingly perhaps, Joe Mantiply and Bryce Jarvis slotted right in behind him.

Among the starting pitchers, Zac Gallen (.366) and Brandon Pfaadt (.377) had the lowest wOBA against on heart-of-zone pitches, but both were higher than league average.

The two most expensive players on the roster, Eduardo Rodriguez, (.479) and Jordan Montgomery (.482) were completely non-competitive when leaving pitches in the middle of the zone. That does not bode well at all for their prospects for 2025.

The are no easy fixes to this. Pitchers can't nibble and be afraid to attack the strike zone. But when the D-backs pitchers attacked, more often than not they were hit hard. Changes in the coaching staff and minor tweaks are unlikely to solve this. It may take wholesale personnel changes, something the team is probably unable to make at this time.