In many respects, Merrill Kelly’s game is as unassuming as they come. His fastball sits around 92 miles per hour. He doesn’t have a true put-away pitch. He doesn’t get an inordinate number of strikeouts or groundballs. But what he’s done for the Diamondbacks since joining the team in 2019 is more significant than you think.

For starters, Kelly’s journey to the majors was anything but ordinary. As a young pitching prospect in Arizona, Kelly was drafted three times: first by the Baltimore Orioles in 2007 out of Desert Mountain High School, then by the Cleveland Guardians in 2009 out of Yavapai College and finally in 2010 by the Tampa Bay Rays out of Arizona State. He signed with the Rays for $125,000 at the age of 21.

Kelly progressed steadily through the Rays’ system, but his lack of raw stuff led his team to believe he was best-suited as a long reliever. He wanted to start. When the SK Wyverns of the Korean Baseball Organization (KBO) reached out with an opportunity to do just that, Kelly decided to go.

Kelly’s KBO numbers don’t necessarily jump off the page. In 119 games (118 starts) over four seasons, he pitched 729.2 innings, posting a 3.86 ERA, 1.31 WHIP, 206 walks and 641 strikeouts.

But he did add a few things: namely, several ticks to his fastball velocity, a cutter that is now arguably his best pitch and a simplified delivery.

By winter of 2018, Kelly was ready to return to the states. This time, it wasn’t going to be in the minors.

One interesting free agent to watch in the coming weeks: 30-year-old right-hander Merrill Kelly, who has spent the last four years in Korea. He is eligible to sign Dec. 1 and will be a rarity: goes to Asia never having played in the big leagues and returns on a major league deal.

— Jeff Passan (@JeffPassan) November 27, 2018

Despite significant interest around the league, the D-backs ultimately signed Kelly to a two-year, $5.5 million deal with team options for 2021 and 2022.

Welcome home, @Mert_723! The #Dbacks have agreed to terms with right-handed pitcher Merrill Kelly on a two-year contract through 2020, with club options for the 2021 and 2022 seasons.

Kelly grew up in Scottsdale and attended Desert Mountain High School, Yavapai College and @ASU. pic.twitter.com/nJvNQAB7lC

— Arizona Diamondbacks (@Dbacks) December 5, 2018

The D-backs recently picked up the second of those clubs options, and for good reason. In 64 starts, Kelly has posted a 4.27 ERA, 1.28 WHIP, 20.2 percent strikeout rate and 6.6 percent walk rate.

Let’s not kid ourselves here: Kelly is not a frontline starter. In fact, he’s almost the exact definition of league-average. In 2021, the league-average ERA and WHIP for starting pitchers were 4.34 and 1.28, respectively—remarkably similar to Kelly’s numbers.

It’s tempting to dismiss Kelly as a net-zero: He doesn’t help you, he doesn’t hurt you. But league-average innings carry a lot of value, particularly for a team like the D-backs where starting pitching depth is lacking and the next man up may be substantially worse. Also, league-average looks pretty good for a team coming off a 110-loss season….

---

Dec. 4, 2018 was a difficult day to be a Diamondbacks fan. On the same day the team signed Kelly for $5.5 million, the Washington Nationals snagged D-backs co-ace Patrick Corbin for $140 million. It was impossible for fans not to see Kelly as the consolation prize.

Since that day, Kelly has posted 4.9 fWAR compared to Corbin’s 6.1 fWAR. While Kelly’s performance has held steady, Corbin’s performance has dipped significantly. In 2021, Corbin posted—by far—the worst ERA of any qualified starting pitcher at 5.82.

According to FanGraphs, Kelly’s 4.9 fWAR equates to $39.4 million of value. That is remarkable, considering the D-backs have paid him just $7.86 million over the past three seasons. That means Kelly has been worth more than five times his salary.

It also means that Kelly has produced $31.54 million of surplus value (the difference between his fWAR-based dollar value and his total pay). Excluding contract extensions, the only free-agent acquisitions with a surplus value anywhere near that mark under general manager Mike Hazen are 2017 signee Chris Iannetta ($16.7 million) and 2018 signee Clay Buchholz (roughly $13 million).

Despite undergoing thoracic outlet surgery last winter, Kelly led the team in innings in 2021, and he was easily the team’s most consistent starting pitcher overall. Given that Kelly is consistently league-average, that probably says more about the D-backs than it does about him.

It also prompts a question that is equally difficult to ponder: Where would the team be without him?

Follow Jesse Friedman on Twitter