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Mariners Add Another Relief Pitcher: Keynan Middleton

Around noon on December 16th, just a day after trading for Rafael Montero and one week after signing Chris Flexen, the Mariners have made another move to bolster their bullpen by signing former Angels pitcher Kenyan Middleton for 1 year, $800K deal plus incentives, per MLB Network’s Jon Heyman.

Middleton has a history with GM Jerry Dipoto, with Dipoto selecting Middleton in the third round of the 2013 First-Year Player Draft back when he was the GM of the Angels. Middleton had this to say about signing with the Mariners:

For an $800K price tag, the Mariners would have been crazy not to take a chance on Middleton for the 2021 season. Middleton has been limited to 37 1/3 IP after undergoing Tommy John surgery in May of 2018, but Middleton has shown many reasons to be optimistic about becoming the player Dipoto envisioned when he drafted him in 2013.

In his rookie year of 2017, Middleton put up very respectable numbers. Pitching in 64 games over 58 ⅓ innings, he logged a 3.86 earned run average (ERA), 4.37 fielding independent pitching (FIP), and an even 4.00 expected FIP (xFIP). Compared to the rest of the league, that was good enough for an ERA- of 90 and a FIP- of 100. Very encouraging for a reliever in his first big league year.

Before having season-ending surgery in May of 2018, Middleton was on pace to assert himself as a dominant bullpen piece for the Angels. He logged 17 ⅔ innings to the tune of a 2.04 ERA and 3.78 FIP, which was good enough for a 49 ERA- and 89 FIP-, earning him the closer role for the Angels. Contrastly, Middleton’s xFIP of 4.82 was not so good, most likely the result of 4.58 walks per nine innings (BB/9) as his home runs per nine innings rate (HR/9) was a low 0.51. The high walk rate could be attributed to battling injury, as his walks in 2018 only became a problem towards the end of April. On May 1st Middleton was put on the IL for right elbow inflammation and appeared in 3 games after being activated, only to be removed mid-game with an injury on May 13th.

In 2019, after recovering from Tommy John surgery, he began his in-game rehab in July pitching in 10 games across the minor leagues, and returning to the MLB stage in late August. Middleton only pitched 16 ⅔ innings in the 2019 professional baseball season.

2020 saw Middleton only pitch 12 innings in 13 games, but the underlying numbers were enough for the Mariners to take a chance on Middleton for the 2021 season. In 2017, his average fastball velocity sat at 96.9 mph, and while his post-surgery velocity was subpar at 94.1 mph, Middleton had his average fastball velocity jump to a career-high of 97.1 mph in 2020; almost equal to his breakout season. His secondary pitches also returned to form, with the slider going from an average velocity of 82.7 mph in 2019 to 87.4 mph in 2020 and the changeup going from 84.1 mph in 2019 to 88.2 mph in 2020.

The movement on his pitches is also trending in the right direction:

The horizontal break on Middleton’s pitches trending to what they were in 2017 and 2018 stands out, showing that he is returning to form and gives hope that there are no lingering issues from his prior injury history and subsequent surgery.

Overall, this signing is a cheap, high-upside move for the Mariners. $800K is chump change for MLB owners, even after revenue losses of the COVID shortened season. Middleton seems excited to be close to his hometown, and the Mariners should be excited to add a piece that very well could be the go-to setup man or closer for them by the All-Star break.

Pitch statistics courtesy of Baseball Savant

Photo courtesy of Icon Sportswire via Getty Images

Garrett Allen

Garrett Allen is a recent college graduate from Valdosta State University and is now pursuing a Masters of Science in Strategic Sports Analytics at the California University of Pennsylvania. Born and raised in Georgia, he is an avid Braves fan and has a particular interest in prospect development.