Postseason Series Win Probability

I would have liked to add this in October, but I had some things to tweak and I wanted to make sure the 2012 data was included at launch.

Thanks to Retrosheet, every single postseason play, game, and series is included. I’ve also added postseason tiebreakers. Before I get emails about the tiebreakers, I realize they are technically regular season games. I just wanted to include them since they are a “loser goes home/winner advances” format.

What I’ve done is incorporate single game win probability into postseason series, to show how each play impacts the team’s probability of winning the series. I’ve set the Home Field Advantage at .559. 55.9% is simply the Home team’s winning percentage throughout postseason history. The reason I included a home field advantage is to show the importance of having an extra home game during a series.

One of my favorite features is the Top Plays list . I’ve tried to include as many filters as possible to narrow down searches. According to my WPA database, Francisco Cabrera’s game winning single in the 1992 NLCS is the biggest series changing play in postseason history. The Braves chances of winning the series before the play was 27%, jumping to 100% afterwards.

But if you apply the “World Series Probability” filter, Hal Smith’s 3-Run HR in the 1960 World Series is the biggest play in history. This filter shows the team’s change in probability of winning the World Series, not just that particular series. Bill Mazeroski’s homerun an inning later is the only Game 7 walk-off in World Series history, but it was Smith’s homerun that is by far the biggest series changing play.

Some other notes from this database….

-The biggest comeback in postseason history was in the 1986 World Series by the New York Mets. In Game 6, with 2 outs and no runners on, the Red Sox had a 99.3% chance of winning the series.

-The second biggest comeback in history was in the same season’s ALCS . This time the Red Sox came back from the Angels’ 99.1% chance of winning.

-The least eventful series, in terms of average change in win probability per play, was the Giants 4-game sweep in the 1989 World Series . All the “excitement” occurred off the field that year.

-Babe Ruth’s caught stealing to end the ’26 World Series was a 10% swing, which is the largest for a caught stealing in World Series history.

-Dave Roberts stolen base in Game 4 of the 2004 ALCS was just the 10th biggest in the 2004 postseason and the 2nd biggest in that season’s ALCS. It only increased the Red Sox chances of winning the series by 1%.

-Derek Lowe recorded the top 2 postseason strikeouts of all-time, both from the 9th inning in the deciding game of the 2003 NLDS . With a 4-3 lead, Lowe struck out Adam Melhuse and Terrance Long, increasing the Red Sox chances by 28% and 26%.

-There have been 46 postseason walk-off homeruns. 9 of those have been series clinching.

-The first postseason walk-off homerun happened in Game 1 of the ’49 World Series (Tommy Henrich).

-Of the 46 walk-off homeruns, the smallest increase in series win probability was Nelson Cruz’s Grand Slam in the 2011 ALCS , just a 2% increase.

-In the “ 2-2-1 Format ” for a 5-Game Series, the home team is just 5 for 15 (.333 Win%) in game 5-s.

– Game 6 of the 2011 World Series has 3 of the top 4 plays from all Non-Clinching World Series games. (1)Freese’s 9th Inning triple, (2)Berkman’s 10th Inning single, (4)Hamilton’s 10th Inning Homerun. David Freese’s 11th Inning walk-off is 22nd on the list.

The Steve Bartman Incident Game 6 of 2003 NLCS
Prior to the play, the Cubs had a 96.0% chance of winning the pennant. Had Moises Alou caught the foul ball, their chances would have increased to 97.6%. Instead, Mark Prior walked Luis Castillo, making their chances 93.6%, a 4% difference. Steve Bartman didn’t walk Luis Castillo, nor did he allow the 8 runs in the inning.

Two batters later, Alex Gonzalez committed an error on a possible double play ball. Before the play, the Cubs chances were 89.7%. Had Gonzalez turned the double play, the inning would have ended with a 97.1% chance. But he committed the error, making the Cubs chances 84.7%, a 12.4% difference.

The Game 6 loss isn’t entirely the fault of Alex Gonzalez, but he had a lot more to do with it than Steve Bartman.

Also, I want to apologize about some of the play descriptions. Most of them are fine, but it’s very difficult to write code for rare plays.

Finally, I don’t currently have data for individual player’s cumulative series WPA. Mainly because I’d like to divide the credit amongst all players without just crediting the batter for offensive plays and pitcher for defensive plays. Unfortunately, I do not have a method for that at the time.