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Wednesday, September 21, 2011
Mariano Rivera, LI, Fangraphs, Rally
Apparently I missed some twitter back and forth between Colin and David and others, trying to figure out how fWAR has him at 39 wins, while rWAR has him at 56 wins.
Here’s how you can come up with the answer fairly quickly. fWAR is FIP at its core. And Fangraphs gives his career FIP- as 62. Since Rivera is at 2.76, that sets the league average at 2.76/.62=4.45 for ERA. Divide by .923 to get into RA9, and we have a league average of 4.82. Replacement level is about 7% higher (for relievers) or 5.16. Because of his short time at starting, the replacement level is really 5.20. Rivera’s 2.76 FIP on ERA scale is 2.99 on RA9 scale. Rivera is therefore +2.21 runs better per 9 IP (5.20 - 2.99). With 1209 IP, that puts us at +297 runs. That’s around 29.7 wins, depending on the runs to win converter.
His LI is 1.87, so we give him 1.435 for WAR purposes. 29.7 x 1.435 = 43 wins. fWAR has him at 39 wins.
Rally however uses runs allowed in rWAR as his core. Both BR and FAngraphs has his ERA at 49% of league average. Since his ER/RA is around the standard league average, we can use his ERA- as a proxy for his RA-. Anyway, so his RA9 is 2.40, and if we divde by .49 we get a league average of 4.90. A league average of 4.90 means 5.24 reliever replacement. Bump that up to 5.28 because of his starts, and we have Rivera at a whopping +2.88 runs per 9IP. With 1209 IP, that’s +387 runs, or 38.7 wins. Multiplying by the 1.435 LI multiplier gets us to 56 WAR. rWAR is showing 56 WAR.
The really big difference originates with FIP v RA9. Rivera is a BABIP machine. It’s a huge difference.
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While you can make the argument that BABIP has little to do with the pitcher at the seasonal level, you can’t make the same argument at the career level.
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