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Thursday, April 09, 2020

Assessing Reliever Value in a Shorter Season

Trying to predict how a reliever will perform from one season to the next can be a pretty frustrating exercise. Some amount of uncertainty surrounds all players, but being a pitcher makes things a little more difficult and being a pitcher who is often asked to throw with max effort with little to no rest complicates further still. And even after we move past those factors, we’re faced with a smaller sample of outcomes for bullpen arms. A 60-inning season is a complete season for a reliever, considerably fewer innings than a starter throws and many fewer batters faced than the number of times most starting position players come to the plate. Trying to predict reliever performance in half a season is even more difficult; attempting to put a value on relievers in a potentially condensed, shorter season becomes quite challenging.

Consider that last season, there were 158 qualified relievers with at least 48 innings pitched. Ken Giles produced 1.9 WAR, ranking 10th in baseball among his bullpen brethren. Brett Martin ranked 60th among relievers with a 0.8 WAR and Matt Albers ranked 130th as a replacement-level reliever. Now, let’s cut those seasons in half. Giles still ranks 10th with just under a win, but he’s now closer to Matt Albers in half a season than he was to Brett Martin in a full season. It is considerably harder to tell, in terms of results, the difference between a good and bad reliever under those constraints. This is further complicated by the fact that the smaller the sample size, the less likely that the results will match the actual performance.

I separated pitchers into three groups from last season: pitchers with at least 100 innings, qualified relievers, and pitchers with at least 20, but less than 40, innings on the season. Then I ran some correlations between WPA, which shows how the actual results on the field mattered to the team, and ERA, FIP, and WAR, to show some measures of performance.

With starting pitchers, we see a good relationship between all three metrics (i.e. the better or worse a pitcher pitched, the better or worse the result was for the team). When we drop the innings requirement down and look at relievers, the relationship gets weaker (i.e. the results vary more, with the pitcher’s performance showing a little more randomness). When we drop the innings requirement down further, we see the relationship grow even weaker. That last set is most representative of the number of innings we might see from relievers in a shortened season.

Once you’ve figured this out, can you teach me how to win big at roulette?

 

QLE Posted: April 09, 2020 at 01:53 AM | 2 comment(s) Login to Bookmark
  Tags: relievers are inherently fungible, shortened season, statistics

Reader Comments and Retorts

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   1. TomH Posted: April 09, 2020 at 06:01 AM (#5937772)
sure, short seasons can make for more variation. 1981:

Rollie Fingers, 1.04 ERA
Goos Gossage, 0.47 ERA, .141 batting average allowed.
   2. Rally Posted: April 09, 2020 at 07:42 AM (#5937776)
Gossage only pitched 46 innings, in line with what you'd expect for a short season. Fingers though pitched 78. Less than his typical 120-130 total, but compared to modern relievers a full workload.

Among closers (20 or more saves) in 2019, only Liam Hendriks (85) had more innings.

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