Arizona Diamondbacks 2024 Player Review: Merrill Kelly

The veteran pitcher endured a lengthy shoulder injury that saw him struggle when he returned before righting the ship

Aug 25, 2024; Boston, Massachusetts, USA; Arizona Diamondbacks starting pitcher Merrill Kelly (29) pitches against the Boston Red Sox during the fifth inning at Fenway Park. Mandatory Credit: Eric Canha-Imagn Images / Eric Canha-Imagn Images

This article is part of a series chronicling the individual seasons of players who appeared for the Arizona Diamondbacks in 2024.

Reviews for players who still have rookie eligibility for 2025 will appear in our prospect season reviews. Players are presented in the reverse order of their aWAR, an average of Baseball-Reference and FanGraphs WAR.

Merrill Kelly, Right-Handed Starting Pitcher, Age: 36

2024 Contract Status: $8.5 MM

Merrill Kelly 2024 and Career Stats / Jack Sommers

The Diamondbacks signed Merrill Kelly out of Korea prior to the 2019 season. Little did they know that he would soon become their longest tenured starting pitcher and one of their best pitchers for over a half decade.

Fresh off helping lead the D-backs to the World Series, Kelly entered the 2024 season with high hopes of fronting a supposed loaded rotation to the playoffs and being the durable veteran that keeps the team in every game he pitches.

That happened to start the season as Kelly started four games from March 29 to April 15 and pitched 24.2 excellent innings. He had a 2.19 ERA, 3.78 FIP, opponent batting average of .200 and walked just six against 21 strikeouts.

It had seemed that Kelly was well on his way to another standout season with the potential for maybe an All-Star caliber season if he kept this kind of pitching up. Unfortunately for him, fate had different plans.

In between his starts, while playing catch, Kelly felt something grab at him in his right shoulder. He alerted the D-backs and they performed an MRI. The results were less than optimal as it revealed that he had a Teres Major strain that left him with no timetable for return.

On April 23, he was placed on the 15-day Injured List before being put on the 60-day Injured List on May 2. That would be where he remained until embarking on a rehab stint on August 6.

In July, Kelly revealed that there were a few things going on in his shoulder beyond just the Teres Major strain and that he was planning to be back by the Tampa Bay road trip in mid-August.

He beat that goal by one start, returning on August 11 in a critical start against the Philadelphia Phillies. Aside from some rust in the first inning, Kelly looked no worse for wear in this start.

He pitched five innings, gave up two runs in a win with three hits allowed, two walks, and two strikeouts. However, his next start would see him begin a run of starts that one typically sees from a player recovering from a shoulder injury.

His velocity was lowered and Kelly struggled with locating all of his pitches. This led to a disastrous outing against the Rays on August 18. Over five innings, Kelly gave up eight hits, six runs, two walks and four strikeouts.

Over his next two starts against the Dodgers and Red Sox, he pitched 11.1 innings and gave up 17 hits, 10 runs, four walks, five homers, and struck out just six batters.

He seemed to right the ship once September came around as he started in San Francisco with a strong seven inning start that allowed just two runs and kicked off a strong run of four starts with less than three runs allowed in each of them.

Over those four starts, Kelly had a 2.45 ERA and 2.89 FIP with 22 innings pitched and just 14 hits, four walks, and 22 strikeouts. He had fixed the home run issue with just two in this time frame compared to five in the prior 11+ innings. Opponents hit just .177 against him during this span.

However, in a start that was deemed a must-win in order to make the playoffs, Kelly faltered on the season's biggest stage. Against the Padres on September 27, he pitched 5.2 innings and gave up eight hits and five runs despite one walk and eight strikeouts.

The five runs were too much for the offense to overcome and with that, Kelly's season ended. He pitched to a 4.03 ERA and an xERA of 4.93. However, his FIP of 4.25 and xFIP 3.89 were better indicators of how he pitched.

Kelly had a true home run problem as he allowed 1.34 per nine innings, the highest of his career since 2020. Over a full season, he had not one season with a higher number. Plus, he struck out batters at a far lower rate than 2023.

In 2023, he struck out batters at a rate of 9.47 per nine innings. In 2024, that number fell to 7.70 as batters made more contact against him. However, he walked fewer batters than each of the prior two seasons. He walked just 2.32 batters per nine innings.

Kelly seemed to have a problem with home runs at Chase Field despite the humidor and large park. He allowed seven of the 11 homers he gave up at home, leading to a 4.19 ERA there compared to a 3.86 ERA on the road.

2025 and Beyond

2025 Contract status: Team Option of $7 MM Picked Up

In July, Kelly spoke on wanting to pitch ten years in MLB and how he hoped to do that with Arizona for the entirety of it. He's guaranteed of getting another year in Arizona and spending seven years with the Diamondbacks after they picked up his team option of seven million dollars for the 2025 season.

With that, Kelly will be back at Salt River Fields come Spring Training ready to go for another season as the No.2 in the rotation in hopes of helping lead Arizona back to the playoffs.

The best news is that Kelly finished the season healthy so he will have a normal off-season with plenty of rest and the chance to start fresh in 2025 without needing to rehab or have a specific return-to-play schedule.

Kelly will be entering his age-36 in 2025. He will need a productive and healthy season to entice the Diamondbacks to give him another contract for 2026 and beyond. Kelly is plenty motivated to make it work in 2025, and achieve his goal of 10 years service time, all with the Diamondbacks.

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