Using a database of play-by-play accounts of (almost -- a few 1972-1973 are missing) every game in the major
leagues 1972-2002, I constructed tables which show
a team's chance of winning a game, based on the score, the inning,
location of baserunners, and number of outs. I have constructed such
tables, one per year, for each year since 1972. In 1996 for example,
if the home team is one run behind in the bottom of the seventh with
1 out and a runner on second, they have a .45253 chance of winning.
These tables are useful in many ways. One use is to determine the value of a player's performance. In the example of the seventh inning situation above, if the runner steals third, the home team's chance of winning improves from .45253 to .49368. This improvement of .04115 is a contribution of the baserunner. If instead the batter had singled to score the runner from second, the home team's chance of winning improves to .58374, and the improvement of .13121 (= .58374-.45253) is credited to the batter. On the other hand, the pitcher's contribution to his team for this event is the opposite, namely -.13121. Had the batter instead made an out without advancing the runner, he would get a -.07986 for lowering his team's chance of a win to .37267, and the pitcher is credited with +.07986.
By adding the value of these contributions of each event for each player over the course of a season, we get
We have no good way of assessing the value of fielding, nor of baserunners distracting pitchers, nor of some baserunning plays. But for hitting (including walking and sacrificing), base stealing, pitching, the system outlined above gives a perfect measure of the value of each player as compared to what an average player would do.
Copyright © 2003 Ed Oswalt
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