Win probability added (WPA) is a sport statistic which attempts to measure a player's contribution to a win by figuring the factor by which each specific play made by that player has altered the outcome of a game.^{[1]} It is used for baseball and American football.^{[2]}
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Week 3 NFL Win Probability for EVERY Game

See a 99.9percent win probability erased in HUGE Conference USA comeback

Winning The Game In The First Inning (part 3)
Transcription
Explanation
Some form of win probability has been around for about 40 years; however, until computer use became widespread, win probability added was often difficult to derive, or imprecise. With the aid of Retrosheet, however, win probability added has become substantially easier to calculate. The win probability for a specific situation in baseball (including the inning, number of outs, men on base, and score) is obtained by first finding all the teams that have encountered this situation. Then the winning percentage of these teams in these situations is found. This probability figure is then adjusted for homefield advantage. Thus win probability added is the difference between the win probability when the player came to bat and the win probability when the play ended.
Some people confuse win probability added with win shares,^{[citation needed]} since both are baseball statistics that attempt to measure a player's win contribution. However, they are quite different. In win shares, a player with 0 win shares has contributed nothing to his team; in win probability added, a player with 0 win probability added points is average. Also, win shares would give the same amount of credit to a player if he hit a leadoff solo home run as if he hit a walkoff solo home run; WPA, however, would give vastly more credit to the player who hit the walkoff homer.
Baseball
MLB postseason
In Game 6 of the 2011 World Series, St. Louis Cardinals' thirdbaseman David Freese posted the best WPA in Major League Baseball postseason history, with a 0.969, which was 0.099 better than the nowsecondbest WPA of .870, posted by the Los Angeles Dodgers' Kirk Gibson in Game 1 of the 1988 World Series. The third and fourthbest WPAs are .854 (by the San Diego Padres' Steve Garvey in Game 4 of the 1984 National League Championship Series) and 0.832 (by the Cardinals' Lance Berkman in Game 6 of the 2011 World Series).^{[3]}
References
 ^ Keating, Peter (2011). "The Next Great Stat". ESPN the Magazine. ESPN. 14 (1): 116–118.
 ^ "Advanced NFL Stats: Win Probability". www.advancednflstats.com. Archived from the original on 20080813.
 ^ "David Freese: now THAT was the best World Series performance in history". BaseballReference.com. Sports Reference LLC. October 28, 2011. Retrieved 20111030.