A look at the Arizona Diamondbacks’ potential Opening Day starting rotation
What could the Arizona Diamondbacks' starting rotation look like at the start of next season?
Zac Gallen
Zac Gallen finished third in National League Cy Young voting and even received a few down-ballot MVP votes. Believe it or not, but 2023 wasn't even the best season of the right-hander's career. That's not to say his campaign was bad, but he could definitely build upon his '23 season and be even better next year.
Gallen pitched 210 innings, working to a 3.47 ERA, 3.26 FIP, and 1.12 WHIP. Gallen struck out 26% of the batters he faced and only had a walk rate of 5.6%. His 0.94 HR/9 rate was also above average. Last season, Gallen was one of only five pitchers to have thrown at least 200+ innings. He was tied with Gerrit Cole among those five arms for the most fWAR at +5.2.
Gallen's season was great, but two factors were slightly worrying: his ability (or inability) to prevent hard contact. Batters owned a 91.5 MPH exit velocity and a 46.2% hard-hit rate against him, both of which were in the 5th percentile or worse. His 9.2% barrel rate was also one of the lowest in baseball. In 2022, he had an 87.8 MPH exit velocity, a 7.8% barrel rate, and a 36.1% hard-hit rate, in comparison.
Gallen's numbers after the All-Star break were good but not great. He only pitched to a 4.03 ERA, 3.94 FIP, and 1.21 WHIP from July 15th onward. Sure, these aren't bad numbers, but the home runs started to catch up to him, and he had a 1.28 HR/9 down the stretch. These struggles carried into the Postseason, as Gallen would allow 17 earned runs on six home runs, 14 walks, and 31 hits in only 33.2 innings.
Still, Gallen could definitely rebound and pitch like he did in 2022 and in the first half of 2023. The right-hander will definitely enter the 2024 season as a Cy Young candidate, as he's now finished top five in voting two years in a row. It will be fun to see what Gallen brings to the table next season atop the Diamondbacks' rotation.
Eduardo Rodriguez
The newest addition to the Diamondbacks rotation, Eduardo Rodriguez, signed a four-year deal during the Winter Meetings. Rodriguez adds another quality veteran rotation anchor and someone who could be an all-star next season, at least based on how he pitched last year and throughout his career.
Rodriguez rebounded from an injury-plagued 2021 season, pitching to a 3.30 ERA, 3.60 FIP, and 1.15 WHIP through 152.2 innings of work. The veteran southpaw had an above-average 23% strikeout rate and posted the third-best walk rate of his career, clocking in at 7.7%. Rodriguez's 0.88 HR/9 rate was also a career-best, but do keep in mind he played in the spacious Comerica Park.
The lefty was slightly above average at limiting hard contact. Rodriguez clocked in with a 7.5% barrel rate, 88.6 MPH exit velocity, and 38.5% hard-hit rate. Although some may be concerned about how he will fare outside of such a pitcher-friendly environment, keep in mind that Chase Field is also fairly pitcher-friendly and that the Diamondbacks' defense was significantly better than the Tigers' last year.
Rodriguez was a great pick-up by the Diamondbacks. The D-Backs really needed a fourth-quality pitcher to add to the rotation, and they went out and got it. He will likely slot in behind Zac Gallen, but don't be surprised if the next guy on our list ends up pitching better than him.
Merrill Kelly
Merrill Kelly silently was an ace-caliber starting pitcher last year. You could make the argument that he pitched better than Gallen. Regardless, Kelly's 2023 season solidified him as one of, if not the most underrated starting pitcher in baseball. It's a crime he didn't receive one Cy Young vote last season.
Through 177.2 innings, Kelly owned a 3.29 ERA, 3.85 FIP, and 1.19 WHIP. While his 9.6% walk rate wasn't all that impressive, he also turned in a 25.9% strikeout rate and a 1.01 HR/9. While Kelly wasn't as bad as Gallen at preventing hard contact, his 89.6 MPH exit velocity and 41.8% hard-hit rate were both below average. Although his 7.8% barrel rate clocked in the 51st percentile among pitchers.
Kelly made up for Gallen's Postseason struggles during October. In 24 innings, Kelly only allowed six earned runs, struck out 28, and only walked eight batters. During his lone World Series start, Kelly fired off seven strong innings, allowing just one run, but struck out nine and, impressively, did not allow a single free pass.
Merrill Kelly has been a great story, going from a career minor leaguer, re-inventing himself in the KBO, and now one of the best pitchers in baseball with Postseason success. Kelly may end up being the best starter in the Diamondbacks' rotation next year. That's a pretty bold statement, but I wouldn't put it past Kelly.
Brandon Pfaadt
Brandon Pfaadt was taken in the very last round of the 2020 draft, which ended up only being five rounds because of COVID. But Pfaadt's development went significantly well. Going into 2023, he was a consensus top 100 prospect, and earned his first extended look in the big leagues.
Pfaadt has a ton of breakout potential. But the bottom line of his rookie season isn't all that impressive. In 96 innings, Pfaadt worked to a 5.72 ERA, 5.18 FIP, and 1.41 WHIP. Although he owned a strong 6.2% walk rate and about average 22.3% strikeout rate, he also allowed over two home runs per nine innings on average with a 2.06 HR/9. A 16.8% HR/FB ratio may suggest that there is some positive regression in Pfaadt's future, but he also had an 11.7% barrel rate.
On paper, Pfaadt's season wasn't great, but he couldn't have asked for a better end to the year. Pfaadt had a 4.14 ERA, 3.89 FIP, and 1.26 WHIP in August and September. While his 1.38 HR/9 was subpar, he had a K% of 25.6% and a walk rate of just 6%. Pfaadt then went on to toss 22 more innings in the Diamondbacks' NL Pennant winning run, striking out 26, only allowing five walks, eight earned runs, and three home runs.
Pfaadt will be heading into his age-25 season, and while he may not be super young, he definitely could keep pitching like he did in the second half and into the Postseason. A lot of young guns don't hit the ground running, and for Pfaadt, it took some time for him to get acclimated to the Majors. But Pfaadt is definitely a candidate for breakout pitcher of the year in 2024.
Tommy Henry
Tommy Henry only made nine appearances in the 2022 season and posted both an ERA and FIP over 5.00. But Henry was given an extended look in the big leagues in 2023, and had it not been for left elbow inflammation that kept him out for most of the second half of the year, Henry may have been one of the Diamondbacks' starting pitchers during the playoffs.
In 89 innings, Henry owned a respectable 4.15 ERA, 4.88 FIP, and 1.36 WHIP. Henry's 1.21 HR/9 was roughly league average, but his 16.8% strikeout rate and 9.2% walk rate were both unimpressive at best. Still, Henry registered an 87.9 MPH exit velocity, 7.6% barrel rate, and 32.4% hard-hit rate. Henry's hard hit rate was in the 89th percentile, and both his exit velo and barrel rate were above average.
But there were still some red flags despite a solid ERA. Henry had a 5.40 xFIP, 5.29 SIERA, and 130 DRA- (95 ERA-). xERA was the only ERA estimator that pointed to relatively solid stats with an xERA of 4.33.
Still, Henry had an ERA+ of 105, making him a slightly above-average pitcher. Henry just needs to pitch like that again to make this one of the best rotations in baseball. That would make five Diamondbacks starting pitchers with above-average numbers in 2024.