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Last night, the Tigers and Red Sox faced off in Game 3 of the American League Championship Series. It was the first meeting between the teams since the Red Sox tied up the series at one game apiece after trailing 5-1 going into the eighth inning. In case your short-term memory isn’t so good lately, that was the game where David Ortiz, a man who has had great troubles in the past during key situations, did this:

In the ninth, a Jarrod Saltalamacchia single to plate Johnny Gomes sent the Tigers home as 6-5 losers. With such a dramatic win, Boston most certainly seized the momentum. Then they won Game 3 by a 1-0 score. Did momentum give them that run?

Before we go any further, what exactly is momentum? The common definition seems to be that it is some sort of circumstance that confers an extra advantage on the team that has “big mo” in its corner. But given that we accept that “momentum can swing with every at-bat,” what’s the point of momentum? If it can be undone by the other team doing something interesting, then perhaps momentum can be better defined as “An alternate formation of the question ‘Which team has done something interesting lately?’” Still, the idea of a big home run conferring some sort of advantage on the momentous team in their next game is a testable hypothesis.

I believe you know what comes next.

Warning! Gory Mathematical Details Ahead!
I found all playoff games from 1995-2012 in which a team entered the batting half of either the eighth or the ninth inning behind, and despite this disadvantage managed to win. This means that at some point, they had a dramatic hit to either tie the game and then untie it (maybe both on the same swing!), which probably made some columnist swoon that they had momentum. Then I looked at what happened in the next game of the series. (Momentous games that closed out a series were not counted.)

There were 51 of these games in the playoffs during this time period, and the momentum-having team won the next game 34 times (two-thirds!) Score one for momentum? No so fast. Teams that have better offenses are better at scoring runs, even in clutch situations. We need to adjust for the fact that momentum might just be a function of having better players mixed with a fortunate set of circumstances for the network covering the series.

Using the log-odds ratio method, I adjusted (based on regular-season stats) for the probabilities that each plate appearance in all playoff games during that time span would end in one of the seven basic outcomes of an at-bat (K, BB, HBP, single, 2B/3B, HR, or out on a ball in play), based on the batter/pitcher matchup (min. 250 regular-season PA for both). I then coded whether there was a team with momentum playing in the game and whether they were the batting or pitching team. I threw everything into a series of binary logistic regressions and let it fly.

Momentum-having teams showed no significant effects in their next game on offense. They hit in line with what might be expected of them based on their own stats and those of the pitcher that they were facing. However, when pitching, momentum-having teams did show a small effect. In the wrong direction. A team that had a big win in their previous game actually saw a small uptick in the number of singles they gave up, while strikeouts fell by a similar amount. It wasn’t earth-moving, but it certainly wasn’t an improvement.

For fun, I looked at situations in which this happened during the regular season during the same time period (1995-2012) and with the same parameters (the two teams had to play their next game against each other). Teams who scored late comeback victories won the next game 51.8 percent of the time, and in this case, the only significant effect was that momentum-having pitchers were less likely to give up extra-base hits. That one seemed apropos of nothing. If there’s something to be said, it’s that there’s little discernible effect of “momentum” from game to game.

The Takeaway
There is little evidence that a dramatic late-inning comeback has any positive effect on the next game of a playoff series. It’s true that teams who experience them are more likely to win the next day, but that seems to be more of a function of the fact that they were probably the better team to begin with. Once again, we find that another favorite narrative is little more than post hoc narrative-building mixed with bad pop psychology.

The common narrative of momentum is that after the game, the losing team feels so devastated by their loss that they can’t possibly go on. The winning team feels so happy that there’s a little spring in their step. Once again, we forget that baseball players do other things than play baseball. I have no doubt that if Game 3 had been played directly after Game 2, there might have been some sad faces taking the field for the Tigers. And yes, there were probably a few words said in the clubhouse that would not be fit for network television. But after that point, the Tigers had the chance to get two nights of sleep, return home, and take some time to either tell each other or realize on their own that Game 3 started at 0-0 (which, as it happens, is close to where it ended).

Baseball teams are small societies, and all societies have ways of both celebrating happy events and mourning losses in a way that enables them to cope with the emotion and move on with life. The idea that the Tigers sat there sulking after the end of Game 2 (or that the Red Sox would simply rest on their laurels) is downright silly and doesn’t give them credit either as professionals or human beings. In that way, I view the momentum narrative as something of an insult to the people involved.

So yes, the Red Sox won Game 3 (albeit barely) after taking Game 2. But it’s important to remember that they had a roughly 50/50 chance of doing so anyway.

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djgx39
10/18
I believe the relevant baseball cliche is "Momentum is tomorrow's starting pitcher."