THE BOOK--Playing The Percentages In Baseball

Wednesday, February 06, 2008

How to calculate WAR

WAR is wins above replacement.  Replacement is defined very specifically for my purposes: it’s the talent level for which you would pay the minimum salary on the open market, or for which you can obtain at minimal cost in a trade.

For nonpitchers, that level is set at -2.25 wins per 162 games, below the average for that league.  Since the same stats of an average AL player is better than the same stats of an average NL player (i.e., the AL is the better league), we have different replacement levels.  Those levels are -2.5 wins per 162 games in the AL, and -2.0 wins in the NL.

The positional adjustments are:
+1.0 wins C
+0.5 SS/CF
+0.0 2B/3B
-0.5 LF/RF/PH
-1.0 1B
-1.5 DH

These are needed so that an average fielding 1B is not valued the same as an average fielding SS.  The DH and PH should be at -2.0 wins (that is, a poor fielding 1B and a DH have the same fielding+positional value).  However, as per The Book, it’s harder to DH, so we give them a 0.5 win boost.  The PH gets an extra 1 win boost over the DH, because PHing is much harder.

For pitchers, that level is set at .380 win% for starters and .470 for relievers.  The exact same pitcher will perform much better in a relief role than in a starter role.  So, you need different baselines.  You can read the relevant chapter in The Book for that.  As with nonpitchers, you need different baselines in each league: .370, .460 in the AL, and .390, .480 in the NL.

For closers, there is a closer replacement level of .570 win%.  Any wins above this level gets multiplied by his Leverage Index (LI).  That is, while he is not responsible for the LI he finds himself in, he is responsible for his talent that allows him to take advantage of the extra leverage (sort of like Ozzie Smith gets to play SS and reaps the benefit of all the extra opps).  We are only giving credit to the closer for the leverage above the .570 win% level.  Credit GuyM for this insight.

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