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The Two Sides of Andrew Chafin

Andrew Chafin

The Two Sides of Andrew Chafin

Arizona Diamondbacks left-handed reliever Andrew Chafin has had a hit-or-miss season so far in 2020. Two of his four outings have been great; the other two have not. There are “fans” calling for his release, with some claiming that “all he does” is walk the first guy he faces and then leave without recording an out. However, these criticisms are unfair, since the numbers do not back them up at all.

(Author’s Note: Before continuing, those who are not familiar with the Goose Egg statistic please see the explanation here by Nate Silver, the inventor.)

The Key – Walking the First Batter

To get a large enough sample size, this study covers all of the 2019 and 2020 seasons. In those two seasons, Chafin has 81 appearances. During those 81, he went 2-3 with 71 strikeouts, 22 walks, two HBP, a 1.399 WHIP, and a 4.31 ERA in 54 1/3 innings. This works out to an ERA-minus of 97, meaning that after adjusting for his home ballpark, his ERA is 3% lower than the league average. He also had 16 Goose Eggs, six Broken Eggs, and 14 Mehs. (In 2019, it was 15-4-14.) The historical average has a ratio of three Goose Eggs for every Broken Egg. So, in 2019, he was above average, but when adding his four 2020 appearances, he’s slightly below average. Overall, however, there is one major factor that causes a Jekyll-and-Hyde difference – walking the first batter.

He walked – or, in one case, hit – the first batter in a grand total of seven of his appearances. In those seven appearances, he had a 3.300 WHIP while allowing five runs, all earned, in 3 1/3 innings. This translated into an ERA of 13.50. He still managed to post two Goose Eggs, but he also had two Broken Eggs and two Mehs.

In his 74 outings where he did not walk or hit the first batter, he struck out 65 and walked 14 while allowing 51 hits over a span of 51 innings. His WHIP was 1.275 and his ERA was 3.71. This translated into an ERA-minus of 83, meaning that his park-adjusted ERA was 17% lower than the league average. He also had 14 Goose Eggs versus four Broken Eggs, a ratio of 3.5 to one.

The Downside of ERA for Relievers

Let’s look more closely at ERA. With relievers, one must be careful with ERA due to its calculation method. It takes a pitcher’s earned runs, multiplies them by nine, and divides the answer by the number of innings pitched. One bad outing can, in the words of Zach Buchanan of The Athletic, “nuke” a reliever’s ERA.

The reason is the whole concept of fractional innings. If a starting pitcher gives up three runs in a seven-inning outing, his ERA is three times nine divided by seven, or 3.86. If a reliever gives up a three-run homer during a one-inning outing, his ERA is three times nine divided by one, or 27.00. If the same thing happens during an outing of two-thirds of an inning, it is three times nine divided by two-thirds. To divide by a fraction, “flip” it (switch the numerator and denominator) and multiply. So, dividing by two-thirds means multiplying by three halves. That means that the ERA is 3 x 9 x 3 ÷ 2, or 40.50. If this happens during one-third of an inning, then it is three times nine divided by one-third, or three times nine times three – 81.00. (Every pitcher who read this probably just screamed in horror.)

In Chafin’s case, his average appearance was two-thirds of an inning. In a bad outing, he usually lasted a third of an inning or less. This means that it does not take long to destroy his ERA. On the flip side, it also means that it can take two or three weeks for him to pitch enough good innings for his ERA to recover from a bad outing.

Andrew Chafin in 2020

As of this writing, Andrew Chafin has four appearances in 2020. His first came on July 25 against the San Diego Padres. He entered the game in the sixth inning with the Diamondbacks trailing by two. He walked the first runner but picked him off first. The other two hitters struck out, giving him a shutout inning.

His third outing was huge. He came into the bottom of the eighth inning on July 28 against the Texas Rangers. The Diamondbacks led, 4-1, but the Rangers had runners on first and second with two out and lefty Shin-Soo Choo at the plate. Chafin struck him out to end the threat and quell most hopes of a rally. A three-strikeout ninth by closer Archie Bradley sealed the victory for the Diamondbacks.

His second and fourth outings did not go well. In his second, he faced the Padres again, entering the game in the bottom of the eighth with the bases empty and the Diamondbacks down by one. The first two batters walked, and the third flied to center, allowing the runner on second to tag and advance to third. Chafin left the game, and the runner on third later scored. This run was Chafin’s responsibility, so this gave him a broken egg. His fourth outing was a disaster. He faced three hitters. The first walked, the second homered, and the third doubled.


As long as Chafin does not walk the first batter, he’s usually fine. As seen by the split in his stats, the danger comes when he walks the first hitter he faces. Since that’s only happened in seven of his last 81 appearances, it is safe to say that the norm is for him not to. This should be good news to Diamondbacks fans, since Chafin is a key part of the Diamondbacks relief corps. With teams relying on their relievers more in 2020 than ever before, the Diamondbacks will need them to perform well if they want to make the temporarily expanded playoff field.

2019-2020 Game Log:

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