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Mystery behind momentum

Is the theory of momentum in football a myth? Stephen J. Dubner takes a looks at the numbers to find out.

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Is momentum a myth?

By Stephen J. Dubner

It's the kind of topic that academic researchers are increasingly interested in -- and the kind that makes a lot of sports fans hate academic researchers.

Why?

Because they take all the fun out of our arguments.

Do we really want to haul out a spreadsheet to talk about whether Mike Smith was wrong to gamble on fourth down? Or whether icing the kicker is a good idea?

As someone who has one foot in both camps (fandom and academic research), I can see both sides of the argument. In the case of momentum, however, I really want to know the truth -- perhaps because it's the kind of phenomenon that is harder to prove than most.

The best place to start is with a famous (for academia) paper from several years ago, called "The Hot Hand in Basketball: On the Misperception of Random Sequences". As you can glean from that snazzy subtitle, the authors come down against momentum, arguing that a "hot streak" is really just a random sequence that we misperceive to be more meaningful than it is.

Ever try flipping a coin 100 times? You'll be surprised at how many long, unbroken sequences of heads or tails you get. It's easy to mistake that for a pattern, suggesting some kind of meaning or momentum, but it's really just a pure illustration of randomness itself. The fact is that if you get 10 heads in a row, the next flip is no more likely to be heads (or tails, for that matter).

And so it is, for the most part, with hot hands and hot streaks and hot quarterbacks. In our momentum video, you'll hear Tobias Moskowitz, the academic co-author of "Scorecasting", discuss how pretty much everyone in football believes in momentum. But, having looked at a lot of NFL data, Moskowitz reaches a sobering conclusion: "There is a much stronger belief in momentum than is warranted by what we see in the data."

In other words, just because a team has driven down the field three times in rapid fashion to set up a dramatic comeback doesn't necessarily mean the fourth drive is sprinkled with fairy dust.

Here's the takeaway: We should be leery of announcers (and coaches and players and fans) talking about "The Big Mo" as if it were a 12th man who suddenly snuck onto the field and is about to streak, uncovered, into the end zone.

Why, then, do so many of us believe that "The Big Mo" is a monster?

Consider one example in our video, the Buffalo Bills' "redonkulous" 32-point comeback against the Houston Oilers in a 1993 AFC playoff game. As Chris "Mad Dog" Russo puts it: "You're gonna tell me momentum had nothing to do with that game?!"

OK, Chris, I'll take a shot at telling you exactly that. You know why we're still talking about that game? Because it was a massive anomaly -- the kind of comeback that almost never happens. It was so rare that our brains have an easy time recalling it. (We do this with all anomalies -- dramatic plane crashes, mass murders, and so on.) And when we recall something so easily, we tend to believe it's far more common that it actually is.

The truth is that you're bound to get a wild 32-point comeback once in a while, just as you're bound to get a streak of 10 or 12 heads-over-tails coin flips. But just as the physical world cannot escape gravity, the statistical world cannot escape what's called "regression to the mean." Those wild streaks, as fun as they were, have very little bearing on what happens next.

Coming up next on Football Freakonomics

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Coming Wednesday, Nov. 23