Football and the Dark Ages
When people discuss American Football these days, it feels like the way people talked about baseball thirty years ago — repeating maxims and rules of thumb that turn out to be untrue. People used to think stealing bases was a lot more useful than it really is. They used to think that walks were meaningless. They used to argue endlessly about whether a low-average power hitter was better than a high-average slap hitter.
We know this stuff now.
In football, we’re still in the bad old days. Take Belichick’s decision last night to fo for 4th and 2 on his own 28, with the game in the balance. This morning, everyone is assuming it was a wild gamble and a blunder.
Nonsense. It’s almost certainly the percentage move on average, and it’s even more clearly the percentage move in context. The Patriots make the first down (winning the game) more than half the time; the league average would be about 60%, the Patriots are better than average, and the Colts defense was tired and is probably not much above average against 4th and 2. So, you're trading a 60+% shot at winning the game right now, for 40 yards of field position with lots of time left, a tired defense, and Peyton Manning waiting on the sideline.
Actually, it wasn’t quite all the marbles, since the Colts had a couple of timeouts left. Still, you could burn all their timeouts and the 2-minute warning and some additional clock. If you don't get another first down, perhaps you run all around the field and waste a lot of time and take a safety and get the free kick. In any case, it’s a big pivot.
In the circumstances, I think you’re comparing these odds with the odds of a Colt interception or fumble in the first 3-4 plays of the next series. (There's also the probability of stopping the Colts on downs, but if you think you can stop them on 4 plays from their 30, you can stop them on 4 from your 30.)
And, in point of fact, the play did work; the refs appear to have blown the spot.
Everyone “knows” that you don’t go for 4th-and-short on your own side of the field, but I’m pretty sure that everyone is simply wrong.