May 22, 2017

Archives for February 2015

In Partial Defense of the Seahawks' Play Calling

The conventional wisdom about last night’s Super Bowl is that the Seahawks made a game-losing mistake by running a passing play from the Patriots’ one yard line in the closing seconds. Some are calling it the worst Super Bowl play call ever.

I disagree. I won’t claim it was the right call, but I do think it was reasonable. Let me explain why.

To analyze the decision we have to put ourselves in the shoes of the Seahawks’ coaches at the time. They did not know that an opposing defender would make a spectacular interception. They knew that was possible—and needed to take it into account—but a fair analysis of the decision can’t use the hindsight knowledge we have now.

With that established, let’s make a simple model of the Seahawks’ strategic choices. They needed a touchdown to win. It was second down, so they could run three plays. The clock was running down, so let’s assume that if they run two running plays, the clock will expire before they can get a third play off; but an incomplete pass on the first or second play will stop the clock and give them time to run a third play. There are three play sequences they can use: run-run, pass-run-run, run-pass-run. (Passing more than once is bad strategy.)

Suppose that a run play with Marshawn Lynch scores 85% of the time, and gets stuffed at the line 15% of the time. If you run twice, there is a 2.25% chance you’ll get stuffed twice, so you win the game with 97.75% probability.

Suppose that passing on second down has these results: score: 50%, incomplete: 49%, interception: 1%. So if you call the pass-run-run sequence, the game outcome probabilities are: score: 97.90%, stopped short: 1.10%, interception: 1%. The odds of winning are a tiny bit better than if you just ran twice.

It’s counterintuitive that passing might be the right choice even though a running play is more likely to score. The reason it comes out this way is that you’re not passing instead of running, you’re passing because passing gets you an extra play and you can still try to run twice, absent a spectacular interception play by the opponent.

Now you can quibble with these probability estimates; and you can argue that the Seahawks might have had time to do three run plays. Change these assumptions, and the strategic calculations are different. But the argument so far should establish that the Seahawks weren’t crazy to pass.

The real kicker comes, though, when we consider the remaining option of run-pass-run. If the outcomes of a pass are still 50/49/1 on third down, then run-pass-run is a clear winner. But maybe a pass comes as less of a surprise on third down, so the outcomes of a pass might be worse. Even so, run-pass-run turns out to be the best strategy. For example, if the outcomes of a third-down pass are score: 25%, incomplete: 73%, interception: 2%, the run-pass-run strategy still scores 98.06% of the time, which is better than either of the other options.

The conclusion that run-pass-run is the best sequence is fairly robust against changes in the probability assumptions. If it’s wrong, it’s probably because of the assumption that run-run-run isn’t an option.

The Seahawks’ decision to pass on second down wasn’t crazy, but a better choice would have been to pass on third down. Announcers who said “just run twice” were giving bad advice. The Seahawks didn’t make a terrible play call; they made a reasonable choice but were defeated by a great defensive play.