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A Perspective of Andrew Chafin

His pitching is good at two levels.

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Andrew Chafin
Andrew Chafin
Photo by Duane Burleson/Getty Images

The Diamondbacks signed free agent relief pitcher Andrew Chafin. Let’s look at him.

How good is Chafin’s pitching?

Several high-level statistics show that over his career he pitched consistently well above average. In 2018, Sean Testerman wrote about Chafin’s FIP, WPA, and RE-24. The following table shows those statistics.

Data from Baseball Reference.

His best season for WPA and RE-24 was 2021. One reason for great results in 2021 was that each of his three main pitches (four-seam fastball, sinker, and slider) had low run values per 100 pitches (-3.0, -1.5, and -1.6 per Baseball Reference). Andrew Chafin’s excellent pitching was noticed.

“Chafin has been downright spectacular this year.” — Ben Clemens, 27 July 2021

Several lower-level statistics show that his pitches challenge batters. For relievers, those statistics include fastball velocity, strike outs per batter faced, whiffs per pitch, and (balls in play plus home runs) per strike. The following table shows that last season Andrew Chafin compared favorably to the other left-handed pitchers for the Diamondbacks. For those measures, Chafin is shown as slightly better than Joe Mantiply who was an All-Star last season.

2022 season except Biddle. Data from Baseball Reference and Baseball Savant.

His best pitch is his slider. In each of the last six seasons, his slider had low run values per 100 pitches. In each of the last four seasons, his slider was better than his 4-seam fastball in three measures: wOBA, whiff percent, and K%. The comparison is shown in the following table.

Andrew Chafin. Data from Baseball Savant.

What percentage of his pitches added a strike to the batter’s count? Last season, it was 40.6%, which was second best of this season’s left-handed Diamondback relievers. Best was Joe Mantiply’s 44.7%.

2022 Season except Biddle. Data from Baseball Savant.

“He [Andrew Chafin] just brings some stability and creates some unity down there [in the bullpen]. He’s got a great way to teach younger players what’s right and wrong, and what’s going to help you and not help you. It’s so simple...” — Torey Lovullo, 28 February 2023

What might be his role in the bullpen?

By a huge margin, for the Diamondbacks Andrew Chafin has the most relief appearances of less than a full inning. In 263 career games for the Diamondbacks, he pitched less than one full inning. Brad Ziegler was second most with 103 games; Mike Meyers was third most with 100 games per Baseball Reference. A big contributor was Chafin’s 86 games with 0.1 innings. Second most was Mike Meyers with 48 games with 0.1 innings. Because of the rule change that each pitcher must face 3 batters (except if the pitcher completed a half-inning or is injured), Andrew Chafin’s 263 games with less than 1 inning pitched may never be exceeded.

Because of his experience, perhaps Andrew Chafin will be at his best in short relief appearances, entering the game when there are one or two outs in an inning.

Last season, 4 of his 5 home runs allowed were in away games. Last season, 14 of his 19 walks were in away games. His ERA and batters’ OPS were worse in away games. Was the difference in performance caused by scouting blind spots of the Tigers? Does his routine change during away games? Does he have a different mindset in away games? In any case, possibly a small change could improve Andrew Chafin’s results in away games.

Does Chafin walk the first batter?

Four AZ Snake Pit articles have expressed concern for how Andrew Chafin pitches to his first batter faced.

“Chafin seems to have struggles with walks when he comes in to face a specific batter but beyond that, he’s been great.”Sean Testerman, 2018

“Now these may all be small sample sizes, however the trend has been so pervasive from year to year, that it’s pretty hard to deny that Andrew has a problem throwing strikes in high pressure situations. His first batter efficiency especially was extremely poor.” — Jack Sommers, 2018

“A running joke at the Snakepit throughout the season was that Chafin wasn’t really ready to pitch until after he walked the first batter. While this was clearly hyperbole, it is a fact that Chafin struggled with the first batter, especially in lower leverage situations.” — James Attwood 2019

“Once the season was finally underway, Chafin did nothing to dispel the narrative of being a walk-issuing reliever.” — James Attwood, 2020

A common theme seems to be, “Does Andrew Chafin walk the first batter he faces?” Let’s look at his 19 walks in 2022.

Slightly more than half (11) walks were to the first batter he faced. Four insights follow:

  • For those 11 batters, their season average OPS+ was 128 (much higher than the OPS+ of 96 for the other eight walks).
  • For the three first-batter-faced who walked with 2 outs, no runners scored that inning. My conclusion is that they were strategically walked.
  • With less than 2 outs, runners scored after 3 of the 8 walks of first-batter-faced. That rate of walks translates to a 73% got-the-job-done, which is great because he faced high-OPS+ batters.
  • My conclusion is that last season Andrew Chafin did not have a problem with walking the first batter he faced. He did walk some high-OPS+ batters, but that is in the context of strategic walks and high first batter effectiveness in preventing runs.

Spring Training Results.

In spring training, two statistics may be good indicators of readiness to pitch during the regular season: strikeouts per batter faced, and (balls-in-play plus home runs) per batter faced. Through 3 March, three relievers struck out at least a third of the batters they faced and allowed half or less of their batters to either put a ball in play or hit a homer. These three best relievers were:

  • .600 SO/BF, .200 (BIP+HR)/BF Tyler Ferguson
  • .556 SO/BF, .444 (BIP+HR)/BF Luis Frias
  • .500 SO/BF, .286 (BIP+HR)/BF Raffi Vizcaino

What were Chafin’s statistics in spring training?

  • .125 SO/BF, .500 (BIP+HR)/BF Andrew Chafin

However, this was a small sample size because Chafin only faced 16 batters through 3 March. I’m confident that his statistics will improve.


Six takeaways follow:

  • For many seasons, Andrew Chafin has been a great relief pitcher. His skill was shown in high-level statistics and lower-level statistics.
  • Andrew Chafin and Joe Mantiply are the best left-handed relievers in the Diamondbacks bullpen.
  • Pitching for the Diamondbacks, Andrew Chafin pitched more games with less than 1 inning than any other Diamondback pitcher. That fact suggests his role may be short relief.
  • Last season Andrew Chafin pitched better at home than away. I hope the Diamondbacks find a way to improve his results in away games.
  • Albeit that this has not always been true, currently Andrew Chafin does not have a problem with walking the first batter he faces.
  • In spring training through 4 March, Andrew Chafin’s results were less than he is capable of. I’m confident that his results will improve to the levels of last season.