How does Eduardo Rodriguez compare to Lucas Giolito?
The Diamondbacks signed free agent Eduardo Rodriguez. Let’s look at whether his performance was better than Lucas Giolito, who is another starting pitcher that the Diamondbacks might have signed.
The following table looks at several performance measures. Eduardo Rodriguez’s metrics look better except for three of my preferred metrics (strikeouts per batter faced, whiffs per pitch, and balls-in-play per strike). Even with a Giolito bounce back, it’s likely that Eduardo Rodriguez will outperform in many metrics next season.
Although it’s possible that Rodriguez will get as many whiffs as Giolito, that’s not bad because Rodriguez is a different type of pitcher.
“Good command and some deception have always been Rodriguez’s calling cards, as opposed to overpowering stuff,…” — Brandon Day, SB Nation
The Diamondbacks’ excellent defense is a good reason to be optimistic that Eduardo Rodriguez results will improve next season.
“He’s usually in the league average range, suppressing home runs pretty well, and in recent years cutting the walks down more. He’s proven to be able to avoid excessive hard contact in the air, but he lives and dies with the defense behind him a little more than the game’s real strikeout artists.” — Brandon Day, SB Nation
Although these two pitchers don’t have the same mix of pitch types, they have three pitch types in common (4-seam fastball, slider, and changeup). For each pitch type, let’s compare whiff percentage, put-away percentage, and hard-hit percentage.
Surprisingly, Rodriguez had higher whiff rates than Giolito on his 4-seam fastball and his slider. With the possible exception of the changeup, Rodriguez’s three pitches were better. That insight (combined with his better metrics) tipped the balance – looking to next season, I expect Eduardo Rodrguez to perform better.
Please note that Eduardo Rodriguez’s slider had better results than his 4-seam fastball. Because his sliders were less than 8% of his pitches, perhaps a performance boost could be achieved by a slight increase in sliders. I’m not the first to note this possibility.
How Does Eduardo Rodriguez Fit in the Rotation?
Eduardo Rodriguez and Merrill Kelly have a very high similarity score of 0.81 per Baseball Savant. Perhaps Eduardo Rodriguez could be considered a left-handed version of right-handed Merrill Kelly.
When the Diamondbacks extended Kelly for two years, Mike Hazen said, “I think the stability that he provides, the pitch mix, his ability to attack different types of hitters — he’s shown that consistently....”
With a very similar Eduardo Rodriguez added to the rotation, perhaps the Diamondbacks have an abundance of stability and consistency.
The following table shows five measures of pitching consistency.
A measure of consistency is the number of quality starts in the last three seasons. Gallen and Kelly have the most (49 and 48). Rodriguez is third with 34. Maybe Rodriguez could have reached 40 without if he had played a whole season in 2022.
A second measure of consistency is, in the last three seasons, how long were their streaks of games with four or less earned runs. They all had two long streaks, with Gallen and Kelly having slightly longer streaks.
A third measure of consistency is, pitching at least 150 innings per year, which is the new standard for an “innings eater.” Looking at the last three seasons, Kelly had 3 seasons as an innings-eater, and Gallen and Rodriguez each had 2 seasons.
Two more measures of consistency are game scores less than 40 (a poor result) and game scores more than 60 (an excellent result). The 2023 ranking for lowest percentage of poor results was Kelly, Gallen, and Rodriguez. The ranking for highest percentage of good results was Gallen, then Kelly barely edged ahead of Rodriguez.
Gallen and Kelly are the most consistent on the five metrics, with Rodriguez in a very respectable third place.
Beyond consistency, it is clear that Eduardo Rodriguez will improve the ERA of the rotation. Two reasons follow:
- Last season his ERA was 3.30, which compared favorably to the average ERA for Diamondbacks starters of 4.67 (data from Baseball Reference).
- His career worst ERA was 4.74 in 2021. Even his career worst season could improve the team (by replacing innings by other pitchers) per the following quote: “The D-backs had the fifth-worst team ERA [5.87 in 314.3 IP] in baseball after their three most-used pitchers, and ranked the worst of any playoff team:” — Dan Szymborski, December 7, 2023
How will the rotation look in 2026?
Mike Hazen has talked about thinking several steps ahead. So let’s think about the 2026 rotation. Remarkably, Eduardo Rodriguez could be the pillar of that rotation.
At that point, it’s likely that two pitchers from the Diamondbacks minors will have established themselves in the rotation. Five candidates are Brandon Pfaadt, Tommy Henry, Ryne Nelson, Slade Cecconi, and Bryce Jarvis.
That leaves two open spots in the rotation. Unless they sign extensions, Zac Gallen and Merrill Kelly will be free agents in the offseason before the 2026 season. If they have eschewed extensions, it is unlikely they will sign with the Diamondbacks. As a result, two pitchers will need to be acquired from outside the Diamondbacks.
The following list shows each pitcher’s status and predicted career innings pitched prior to the 2026 season.
- Zac Gallen, free agent, 1800 predicted career innings pitched.
- Merrill Kelly, free agent, 2470 predicted career innings pitched.
- Eduardo Rodriquez, signed through 2027/28, 2165 predicted career innings pitched.
- Pfaadt/Henry/Nelson/Jarvis/Cecconi, pre-arb, each with less than 1000 predicted career innings pitched.
In summary, there are four reasons to be optimistic about the Eduardo Rodriguez acquisition.
- Next season, Eduardo Rodriguez will likely outperform Lucas Giolito (a bounce back alternative).
- Eduardo Rodriquez adds stability and consistency to the rotation, although his very respectable consistency (in the 5 measures of consistency) is generally below Zac Gallen and Merrill Kelly.
- Eduardo Rodriguez will almost certainly improve the rotations’ average ERA because his ERA is much better than last season’s average ERA.
- Remarkably, unless events intervene, in 2026 Eduardo Rodriguez could be the pillar of the rotation.