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. It is used for

baseball Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding tea ...

and

American football American football (referred to simply as football in the United States and Canada), also known as gridiron, is a team sport played by two teams of eleven players on a rectangular field with goalposts at each end. The offense, the team with ...

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 Retrosheet is a nonprofit organization whose website features box scores of Major League Baseball (MLB) games from 1906 to the present, and play-by-play narratives for almost every contest since the 1930s. It also includes scores from every major ...

, 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

home-field advantage In team sports, the term home advantage – also called home ground, home field, home-field advantage, home court, home-court advantage, defender's advantage or home-ice advantage – describes the benefit that the home team is said to g ...

. 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.

Win probability and win shares

Some people confuse win probability added with win shares, 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 lead-off solo home run as if he hit a walk-off solo home run; WPA, however, would give vastly more credit to the player who hit the walk-off homer.

Baseball

MLB postseason

In Game 6 of the 2011 World Series, St. Louis Cardinals' third-baseman

David Freese David Richard Freese (born April 28, 1983) is an American former professional baseball Infielder, infielder in Major League Baseball (MLB). He began his MLB career with the St. Louis Cardinals, where he was a key player during the 2011 Major Leag ...

posted the best WPA in Major League Baseball postseason history, with a 0.969, which was 0.099 better than the now-second-best WPA of .870, posted by the Los Angeles Dodgers'

Kirk Gibson Kirk Harold Gibson (born May 28, 1957) is an American former professional baseball player and manager. He is currently a color commentator for the Detroit Tigers on Bally Sports Detroit and a special assistant for the Tigers. As a player, Gibson ...

in Game 1 of the

1988 World Series The 1988 World Series was the championship series of Major League Baseball's (MLB) 1988 season. The 85th edition of the World Series, it was a best-of-seven playoff played between the American League (AL) champion Oakland Athletics and the Na ...

. The third- and fourth-best WPAs are .854 (by the San Diego Padres'

Steve Garvey Steven Patrick Garvey (born December 22, 1948) is an American former professional baseball player. He played in Major League Baseball as a first baseman for the Los Angeles Dodgers and San Diego Padres from 1969 to 1987. Garvey was the National ...

in Game 4 of the 1984 National League Championship Series) and 0.832 (by the Cardinals'

Lance Berkman William Lance Berkman (born February 10, 1976), nicknamed "Fat Elvis" and "Big Puma", is an American baseball coach and former professional baseball outfielder and first baseman, who is the current head baseball coach of the Houston Christian Hu ...

in Game 6 of the 2011 World Series).

References

{{Baseball statistics Baseball statistics