Almost everybody does it. When an MLB team trailing in a postseason series pulls out a big win, we say — or we think, or we write, or we at least consider — that the series’ momentum has swung.
It makes obvious fodder for discussion for anyone following postseason baseball, from the casual fan at the water cooler to the seasoned analyst on television. I’ve certainly been guilty of it myself, and anyone eager to prove me a waffling fool upon reading this post could dig up countless examples of this author stating — in print, online, in radio interviews, in real-life conversations — that playoff wins like the Yankees’ series-evening victory in Boston on Saturday might represent some greater change in the course of the series.
One issue: The notion of “momentum” inside a short MLB postseason series does not exist, or at least seems impossible to identify with any evidence beyond the anecdotal. The truth more likely lies with the old baseball adage, attributed to longtime manager Earl Weaver, that momentum is as good as the next day’s starting pitcher.
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Lacking both the time and the mathematical aptitude to pursue this in any more exacting way, I looked back at every postseason series from 2012 through 2017 to see if I could find any indication that momentum is a real thing. I tallied the number of times a team that won any game in a series won the next game in the series, which, I think, makes at least a decent back-of-the-napkin indicator for momentum.
There’s a big, fun reveal coming in a minute. Stick with me.
I just want to clarify the methodology: I essentially totaled the won-loss record of teams coming off a postseason win. The first game of any series, here, establishes the momentum, but does not reflect whether momentum helped a team. So in the instance of a four-game sweep of a seven-game series, the team with momentum went 3-0. In a series like last year’s Cubs-Nationals NLDS, in which the Cubs won Games 1, 3 and 5, the team with “momentum” went 0-4.
I suspect one could go back through most of MLB postseason history and return similar results, but I used 2012 as an endpoint for a couple reasons. For one, that was the first year of the current postseason format, in which two Wild Card teams per league play for entry into the proper playoffs. I did not incorporate the results of Wild Card games into the tally, since I was looking for evidence of momentum inside discrete series.
From 2012 to 2017, there were 204 total MLB postseason games across 42 playoff series. Since Games 1 did not count for this exercise, that leaves exactly 162 games in which one club had momentum within a series, and baseball fans are very good at digesting information presented in 162-game samples.
Ready for this?
In 162 relevant games between 2012 and 2017, teams coming off a win in the series were 80-82 in the following games.
Momentum, as we define it, means nothing. Again: 80-82. Eighty and eighty-two.
The team with momentum, so to speak, inside a postseason series wins the next game only about half the time, and this really shouldn’t come as much of a surprise. The odds on any individual baseball game between two good teams are pretty much a coin-toss. Mathematician Leonard Mlodinow’s well-reasoned claim — documented in this space countless times — is that it would require a best-of-269-game series to prove one MLB team capable of beating another one 55% of the time. Even if postseason teams do get some boost from winning the previous night’s game, it’s not enough to overwhelm the randomness that dominates baseball, and so it’s not enough to reliably impact the next day’s final score.
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