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# Pro Football Reference Blog

## Checkdowns: Belichick Was Right

Posted by Neil Paine on November 16, 2009

I had a feeling about this at the time, and Brian Burke of Advanced NFL Stats only confirms my initial belief: if you crunch the numbers, Bill Belichick made the correct decision when he decided to go for it on 4th-and-2 at his own 28 with 2:08 to go in the game vs. Indy last night...

"With 2:08 left and the Colts with only one timeout, a successful 4th-and-2 conversion wins the game for all practical purposes. A conversion on 4th-and-2 would be successful 60 percent of the time. Historically, in a situation with 2:00 left and needing a TD to either win or tie, teams get the TD 53 percent of the time from that field position. The total win probability for the 4th-down conversion attempt would therefore be:

(0.60 * 1) + (0.40 * (1-0.53)) = 0.79 WP (WP stands for win probability)

A punt from the 28 typically nets 38 yards, starting the Colts at their 34. Teams historically get the TD 30 percent of the time in that situation. So the punt gives the Pats about a 0.70 WP."

And if you consider that Manning is an assassin from anywhere on the field, it will actually make it look like a better decision by Belichick. As Brian says, "you can play with the numbers any way you like, but it's pretty hard to come up with a realistic combination of numbers that make punting the better option. At best, you could make it a wash."

Now, I know Rodney Harrison and Trent Dilfer were ripping Belichick pretty hard on TV, but that's only because hindsight is 20/20. Had the conversion succeeded, they would have praised the coach for his "guts" and "decisive leadership". It's the great thing about being able to analyze decisions like this after the fact -- you can tailor your analysis to fit the result, rather than what the right choice was at the time. Unfortunately for Belichick, he didn't have that privilege. But maybe he can take some solace in knowing that, statistically, he made the right call, talking heads be damned.

EDIT: Here's an Excel sheet where you can enter the probabilities you think were correct last night, and see how often the Patriots would win. "1stDprob" is the probability of getting the 1st down on 4th-and-2; "1stdwp" is the Pats' win probability if they convert on 4th-and-2; "failed1stdcltwp" is the Colts' win probability if the Pats' 4th-and-2 fails; "puntprob" is the probability of the Pats getting off a punt; and "coltsdrvwp" is the Colts' win probability if Belichick punts and asks them to drive down the field. As you can see, even if you believed that Indy would win 70% of the time if you failed on 4th-and-2 and only 30% if you punted, it still comes out a wash... There's no doubt Belichick made the right decision.

This entry was posted on Monday, November 16th, 2009 at 7:09 am and is filed under Checkdowns. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.