Welcome to another edition of “Positive & Negative Regression,” where we dig into some analytics each week to identify two players due to heat up and two likely to cool down. Today we’ll turn to the bullpen and look at a few relievers whose YTD performance may not be what it seems.

As mentioned a few weeks ago, comparing ERA to FIP is a quick and easy way to look for regression during the season. Taking this one step further is to compare ERA- to FIP-. If you are unfamiliar with these stats, they are simply ERA and FIP adjusted for home park and league and put on a scale with 100 being average. So like ERA and FIP, the lower, the better for ERA- and FIP-. You can find a more detailed explanation on Fangraphs if you are so inclined.

In addition to the “minus” stats being a bit more accurate, they are easier to compare than straight ERA and FIP as everything is on the same scale. Subtracting ERA- from FIP- gives you a number, and just like the variables themselves, the lower the number, the better.

So with that in mind, below are two relievers with high negative FIP- minus ERA- differences who appear to be candidates for positive regression. Conversely, two with high positive differences may lead to some negative regression. As always, if you need help with some of the statistics mentioned below, check out our Sabermetrics Glossary, and please note that all stats are through Saturday, June 25.

Positive Regression Candidates

Craig Kimbrel (RP – LAD)

Kimbrel has only blown one out of fourteen save attempts this season, and his K/9 rate of 13.7 is excellent. However, he’s sporting a 4.30 ERA and a 1.52 WHIP, which are high enough to make fantasy managers nervous. So what is going on with him?

For starters, his walk rate is a bit high at 4.30 per nine, though not crazy above his career average of 3.63. He’s also been a bit unlucky as players have a .404 BABIP off him when they put the ball in play. On top of that, his LOB% of 66.5% would be the worst of his career. It appears that not only are more runners reaching base off him, but they are also scoring at a higher rate.

The good news is, as the table above illustrates, Kimbrel’s FIP and FIP- are pretty good, as is his xERA, which is 2.76. So unless something changes, he’s likely to rebound, making him an excellent buy-low candidate. In addition, with the recent loss of Daniel Hudson for the season and with Blake Treinen still out for another month or so, he should get a lot of rope from Dave Roberts.

Diego Castillo (RP – SEA)

Castillo had a rough May, especially one three-game stretch where he gave up nine earned runs over a combined one-inning pitched. He’s righted the ship in June, though, with an ERA under 1.00 in ten innings this month. Two of his four saves have also come this month, and it appears the Mariners are using him in that role more often.

As the table indicates, his FIP and FIP- are much better than the league average. Castillo also sports a 1.19 WHIP and 10.4 K/9, which are solid. He’s still in a committee and probably will remain in one; however, Castillo could be a bargain as a cheap option for saves and holds.

Negative Regression Candidates

David Robertson (RP – CHC) 

Robertson has been a great comeback story in 2022, emerging as the Cubs’ closer and racking up nine saves. However, he may cool off a bit in the ERA department in the coming weeks. His FIP and FIP- are still better than league average, but they don’t paint near as rosy a picture as his ERA and ERA-.

Robertson’s BB/9 is 4.23, similar to Kimbrel’s, but he’s held opposing batters to a low .193 BABIP. Thus, runners aren’t getting on base as often as they may down the road. In addition, he’s working out of a lot of jams, with a 92.7% strand rate (LOB%). This should normalize in time as well.

Robertson will probably retain the closer’s role, but expect some regression with him and sell him high if you can. Especially since the Cubs may go into sell mode next month, leaving save opportunities even harder to come by down the stretch.

Colin Poche (RP – TB) 

Poche is yet another relatively obscure reliever to emerge in the Rays’ bullpen. He’s tied with Andrew Kittredge for the team lead in saves with five and for the team lead in holds with nine. He’s been a pleasant surprise for fantasy this season, but his FIP and FIP- suggest it may not last.

Of the 180 relievers we pulled with 21 or more innings pitched this season, Poche had the highest variance between ERA- and FIP-. It appears he’s been the recipient of some luck. He has a low BABIP of .148 against him and a high LOB% of 87.5%. Lately, he’s been a good source of saves, with five in the past month, but don’t be surprised if this doesn’t continue.

Poche’s ownership % is still relatively low, so it’s not like you can call him a sell-high candidate. However, if you consider adding him, keep the above in mind, and don’t be afraid to cut and run at the first sign of trouble.

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