Joe Mantiply Had an Uneven 2023 Season, but Finished Strong

The left-handed reliever was sent down to Reno multiple times, but returned strong down stretch to help D-backs bullpen

This article is part of a series of player reviews for the 2023 Arizona Diamondbacks. It was a surprising and marvelous year for the team as they won 84 games to make the postseason. They advanced to Game Five of the World Series before bowing out to the Texas Rangers. There are 54 players in all that had at least one at-bat or pitched at least one inning for the team this past season. They are being presented in reverse order of their aWAR (average WAR-Wins Above Replacement) produced, which is the average of Baseball Reference and Fangraphs WAR. These are their season stories.

Joe Mantiply had a tough 2023 by his standards, but it was only slightly worse than his career numbers / Jake Oliver

Joe Mantiply was coming off an All-Star 2022 season as he entered the 2023 regular season. He was set up to be Manager Torey Lovullo's most trusted bullpen arm and best left-handed pitcher. Unfortunately for Mantiply and the Diamondbacks, that failed to come to pass. While his season-ending stats were average in terms of MLB talent, they weren't close to his dominant 2022. His ERA was nearly two runs higher, and his innings dropped by 21, thanks to being optioned to the Reno Aces and Triple-A, and an injury. His FIP was a run higher and his xFIP was nearly two runs higher. However, was his 2023 season truly as bad as it seemed?

His season got off to a rough start owing to left shoulder inflammation. He didn't make his season debut until April 18th. He would appear in eight games until May 12th. Over that span, Mantiply was his typical strong self with a 2.35 ERA, 2.86 FIP and eight strikeouts over 7.2 innings and eight games. However, he would go back on the Injured List, this time due to a right hamstring strain.

Mantiply returned on June 12th, but consequently struggled mightily. He allowed 11 hits, eight runs, and had just six strikeouts in five games and eight innings. Due to that, the D-backs optioned him to Triple-A and the Reno Aces in hopes of getting him sorted out. 

With the Aces, Mantiply had a 7.30 ERA over 11 games and 12.1 innings with four walks and 11 strikeouts. He wouldn't return to an MLB mound until getting called up August 1st, following the Andrew Chafin trade.

Mantiply stayed with the D-backs for the entirety of August and saw limited success. While he had mostly clean outings, two bad outings in which he allowed two and three runs, respectively, inflated his already rough ERA. Still, he pitched 10.1 innings and had three walks to six strikeouts. While his ERA was a bad 6.97, his FIP was 4.22. That indicated that he had been better than what the baseline results were.

The Diamondbacks kept him on the active roster for September, putting Mantiply in mostly low-leverage situations. That worked like a charm for him. September was his best month since April. Over 13 innings and 10 games, he allowed just two runs, had eight strikeouts, and had a 1.38 ERA. His FIP was a strong 3.18, mostly due to five walks given up.

This was enough to put Mantiply on the postseason roster where he served as a low-leverage reliever and an opener. He started the playoffs hot with three straight scoreless outings against the Brewers and Dodgers. He encountered some difficulties in Game Two of the NLCS when he gave up three runs in just 0.1 innings. However, he righted the ship and allowed just one unearned run over his next four outings and 3.1 innings. That included his Game Four NLCS opener start. Mantiply would pitch in the World Series twice, including the ill-fated Game Four opener start. He would allow a run in 1.1 innings in a game that completely swung the momentum of the series to the Texas Rangers.

Still, it was a strong and encouraging finish to a tumultuous season that was the most difficult of Mantiply's career with the Diamondbacks.

2024 Status and Outlook

Joe Mantiply is entering his age-33 season. It will be his fifth total season with the Arizona Diamondbacks. He first appeared in an MLB game as a member of the D-backs in 2020. However, thanks to multiple send-downs and limited MLB experience prior to the Diamondbacks, he still has three years of control. This off-season will see the D-backs go through arbitration for the first time with Mantiply. He will have two more go-rounds with the panel until reaching free agency after the 2026 season. That is if he isn't sent down for any prolonged time like in 2023. Thanks to being a reliever, his salary is projected for $1 million in 2024.

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