September 7, 2006

Lies, Damned Lies

What to Do With Papelbon

by Nate Silver

Since 1946, there have been exactly 100 pitchers who pitched at least 80% of their innings in relief after having pitched at least 80% of their innings as a starter in the previous season (minimum 50 IP in year n and 100 IP in year n-1). Sometimes, these were pitchers like Rick Aguilera who were returning to relief work after a failed experiment in the starting rotation; others were journeymen who teetered between starting and relief roles throughout their careers. For the most part, though, these were former starters, who became relievers more or less permanently.

The good majority of these pitchers improved their ERA, as well as their peripheral statistics, upon making the jump to the bullpen. But this should be no surprise. As I described last week, if you take a starter whom you know nothing else about, you can expect him to knock about 25% off his ERA when he pitches in relief. The question, then, is whether there are any similarities among the pitchers that improved their ERA by more than 25% once joining the bullpen.

In order to tackle this question, we’ll compare two things:

• The pitcher’s baseline EqERA projection, as given by PECOTA. Note that these are not 'full' PECOTAs, as they do not go through the comparables stage of the analysis. Nevertheless, the baseline forecast will account for a pitcher’s key peripheral statistics, regress to the mean as appropriate, and remove noise due to park effects, league effects, and defense. Note that the baseline forecast assumes that the pitcher remains a starter.

• The pitcher’s actual, "role-adjusted" EqERA. The role adjustment is accomplished by taking a pitcher’s EqERA, and converting to it to what we’d expect the EqERA to be if he pitched 100% of his innings as a starter. For a pitcher who throws all his innings in relief, the "role-adjusted" EqERA will be roughly 25% higher than the regular EqERA.

These ten pitchers took the most advantage of their new role:

Pitcher          Year       EqERA        Role-Adjusted  Improvement
                            -PECOTA         EqERA
-------------------------------------------------------------------
Goose Gossage    1977         3.96           1.89         210%
Eric Gagne       2002         4.42           2.39         185%
Mike Remlinger   1999         4.38           2.53         173%
Jeff Russell     1989         4.75           2.89         164%
Dave Leonhard    1969         4.92           3.05         161%
Wayne Twitchell  1976         4.43           2.76         160%
Tom Gordon       1998         4.04           2.53         160%
Hal Woodeschik   1963         4.74           3.07         154%
Jose Jimenez     2000         4.32           2.89         150%
LaTroy Hawkins   2000         4.96           3.32         150%
    

Many of these names will come as no surprise, and the list includes some famously successful bullpen conversions like those of Eric Gagne and Tom Gordon. We also see our friend Goose Gossage. These pitchers represent all sorts of different age groups; Gagne was 26 in 2002, while Mike Remlinger was 33 before the Braves figured out that he’d be an effective set-up man.

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