### Background

Joe Sheehan was allowing the possibility that chemistry exists (it does, so no reason to pretend it doesn’t) and that he may have found it. Did he? Chemistry and momentum are two of those things that people will point to after something good has happened, and will forget about if something bad has happened. This is like you go to Vegas, tell your friends you won $10,000, conveniently forgetting about the previous time you went when you lost $20,000. There are other examples in sports. Like the Pujols/Lidge/Oswalt contrarian situation. Or the more famous Don Cherry too-many-men situation, or Ronaldo’s injury making everyone on the team bleak before the final game, or the stolen World Series in 1985. We tell the $10,000 wins stories a lot more than the $20,000 losses.

Now, let’s say that you somehow are god-like, and know momentum when you see it. How much is it worth? As we know, a superstar like Albert Pujols is worth some seven wins, per 162 games, above replacement. That means that if you have a .500 chance of winning with an average team and bad first baseman, adding Pujols will make it a .550 team. Something like that. If you have a great pitcher, C.C. Sabathia or Doc Halladay, you turn a .500 team into a .625 team. How much can momentum be worth? Can it possibly cancel out the Rays bringing in C.C. Sabathia or Roy Halladay? Can it even cancel out bringing in Grady Sizemore or Pujols or Joe Mauer? Is momentum even worth Willie Bloomquist?

One of my readers suggested that in-game momentum should be easier to find, and have more impact, than day-to-day momentum. Makes sense. After all, as Earl Weaver once said, momentum is tomorrow’s starting pitcher.

### The Study

I looked for every single game in the last 50 that a home team came back from at least five runs down to tie the game and end the inning. This means that, starting the top half of the following inning, we’ve got two teams tied, each with an equal number of outs to go, except the home team now has the momentum. What happened? How often did the team with the momentum win the game?

By my count, there are 230 such games, of which the team with the momentum won 126 times, for a win percentage of .548. That’s pretty good. But, is this simply the home field advantage speaking, or is it momentum? Here is how the home team did, when coming back from down by five runs, down by between one and four runs, and tied (i.e., they didn’t score in the inning of a tied game):

Down by… Eventually wins…

5 or more .548

1 to 4 .528

0 .524

So, we see that there is a mild gain to momentum: a +.020 improvement in winning. Given 230 games, one standard deviation is .033. One cannot even claim that the result has much statistical significance (less than one standard deviation from the mean). But, I know most of you don’t want to talk about statistical significance. Let’s take the results for what they are: the home team, if it is down by at least five runs but ends the inning tied, will eventually win the game 54.8% of the time, while in all other non-momentum situations, they will win about 52% or 53% of the time.

Let’s repeat, but this time with the road team having the momentum. Note that entering the bottom half of the inning means that the home team has three extra outs for the game. So, we should expect to see lower win numbers for the road team. Down by five or more to tie the game entering the bottom half of the inning, the road team eventually wins 67 of their 153 games, or a win percentage of .438. Here is the full chart for the road team having momentum:

Down by… Eventually wins…

5 or more .438

1 to 4 .396

0 .403

We have a similar situation here as with the home team: The effect of momentum is an extra .035 wins or so.

### Summary

If we combine the two results (home and road), we get that the team with the momentum wins 193 out of 383 games, or .504. We need to compare that to some baseline. Since there were 230 games with the home team having the momentum, and we expect them to win around .524 times without momentum, then the number of non-momentum wins per 230 games would be roughly 120.5 wins. Similarly, with 153 road games with the momentum, we would have expected around .403 wins with no momentum, or 61.5 wins per 230 games with no momentum. Combining the two baselines, we have 182 wins in 383 games, or a .475 win percentage rate expected with no momentum.

If I also consider the inning, the baseline level is a .467 win percentage expected with no momentum. The difference between the actual win percentage with momentum (.504) and no momentum (.467) is +.037 wins. (This figure is almost 1.5 standard deviations from the mean.) That is the extent of the momentum effect, in-game. Momentum is, at best, like getting one superstar player on your team. (Statistical significance tells us it is much less than that. But, I know you don’t want to hear that.)

And don’t forget that we’re talking **extreme** momentum here; in-game momentum in which the team scored five runs in an inning to tie the game. One must believe that the effect of momentum must be even less day-to-day.

Momentum exists. But we’ll be hard-pressed to find it in anything other than in-game scenarios. We can barely find it with the numbers in even the most dramatic come-from-behind games. All you have left to do is enjoy the moment, without having to explain it. If you really have the need to tell people that you have found momentum, then here’s what you do: Find 10 games from now for the next 12 months that you think has momentum or chemistry written all over it. Bet on the game. Then, come back here, on November 1, 2009, and tell me how much money you made. And I don’t want to hear only from the winners.