Reddit reviews Smart Baseball: The Story Behind the Old Stats That Are Ruining the Game, the New Ones That Are Running It, and the Right Way to Think About Baseball

Keith Law. https://www.amazon.com/Smart-Baseball-Behind-Ruining-Running/dp/0062490222/

u/sigbox here is a reply for now from my partner:

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Win Probability Added (WPA)

We will be publishing a full article comparing the WPA statistic with the RunPlusMinus RPM statistic.

Wikipedia defines WPA as a sport statistic which attempts to measure a player's contribution to a win by figuring out the factor by which each specific play made by that player has altered the outcome of a game. Fangraphs gives a good description of the WPA statistic here and contains references to related articles. As well, Keith Law’s book “Smart Baseball” devotes a whole chapter to WPA.

The RPM statistic measures the contribution of every player’s involvement in every play relative to the historical average contribution of a player in the same role in that game situation. The most succinct way of comparing WPA and RPM is to show the differences when considering their respective adherence to the 5 “CRAZI” principles described in the post “The Best Baseball Statistic”. These are summarized in the table below. The forthcoming article will provide much more detail on each principle.

|Principle|RPM|WPA|
|:-|:-|:-|
|Comprehensive|Yes (all players & events)|No|
|Run-Based|Yes|No (win based)|
|Additive|Yes (player & team)|Yes* (player only)|
|Zero-Sum|Yes|No (average is zero)|
|Independent|Yes|Yes|

The applications of RPM are more extensive than those of WPA. Specifically, RPM results can be used to: assist in-game decision making, predict game winners with more than 50% accuracy, forecast team standings, suggest fair salaries, rank all players and teams on both total and component (batting, running, pitching, fielding) performance.

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I hope that helps!

- Ivan