Up 7 late – should you go for two?

During two of the last three Sunday Night Football contests, one of the participating teams scored in the final few minutes of the fourth quarter to take a 7-point lead. At those points in the game, both Denver (last night) and Seattle (two weeks ago) were faced with the decision to kick the extra point, thereby likely securing the 8-point advantage, or to go attempt a two-point conversion, thus taking a (roughly) 50-50 chance at a two-possession lead.

What’s the optimal strategy?  It’s a tough question, so I posed this on Twitter.

Roughly 50% of my respondents (overall, a more analytic-friendly crowd) answered that, yes, teams should go for two, with the remaining voters equally split between “No” and “It depends.”

In this post, I’ll suggest that, at least empirically, it hasn’t made a ton of difference one way or the other.

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In considering the optimal two-point strategy with a seven-point lead, we can start by looking at how often teams have come back when trailing by seven, eight, or nine points. While there are hundreds of games where teams have scored and kicked an extra-point to build exactly a seven-point lead late in the game, it’s a bit dicier to find examples of teams scoring and taking a seven-point lead before kicking the extra point. Using Armchair Analysis’ data, for example, there were just 88 such examples between 2000 and 2015.

So instead of looking at those 88 games, I expanded the analysis to include any game where a team took possession in the final eight minutes of the fourth quarter between 10 and 40 yards from their own goal when down either 7, 8, or 9 points. In essence, this adds about 1300 contests (so 1400 total) that should be equivalent to a team trailing late in the game having just given up a touchdown.

Here’s how the games eventually played out. The chart below shows the fraction of times that the winning team held on, depending on the size of their lead. The size of each dot is proportional to the number of games with teams in those situations. I also used two colors to vary when the offensive team started its possession.

Screen Shot 2016-11-28 at 1.14.32 PM.png

Teams ahead by seven points have won about 86% of games when starting a possession on defense with between 4 and 8 minutes left, a number that jumps to 89% when up eight and 94% when up nine points. This makes sense. If you have a larger lead, you are more likely to win.

And there’s a similar increase for teams getting the ball in the final four minutes of a contest (shown in red). In fact, in the 94 games when a team has started a defensive possession with fewer than 4 minutes left when ahead by exactly nine points, they’ve won all 94 times. That isn’t to say that teams can’t lose when ahead by this margin – they’ve lost when up by 10, for example – but it’s quite unlikely. A two-possession lead late in the game is really hard to overcome.

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We can use the probabilities above to outline a strategy of whether or not to attempt the two-point conversion.

For teams scoring with between 4 and 8 minutes left, we are left with the following calculation:

Go for two (assuming a 50% chance of a successful conversion):

50% chance to get a 94% chance of a win + 50% chance to get an 86% chance of a win = Win 90% of the time

Kick:

Win 89% of the time.

Using these numbers, there’s a *slight* advantage to going for the two-possession lead by attempting the two-point conversion. Given the associated errors that come with these probabilities (the margins of error in the graph, for example, are about 4%), this difference is not statistically meaningful.

For teams scoring with between 0 and 4 minutes left, we use the following calculation:

Go for two: 

50% chance at a 99% chance of a win (best guess) + 50% chance at an 89% chance of a win =  Win 94% of the time

Kick: 

Win 93% of the time.

Again, very little difference, and not a statistically meaningful one.

Altogether, there’s little empirical evidence to suggest that teams should attempt the two-point conversion late in the game when up seven. While there may be a slight advantage to the more aggressive strategy, it does not appear to be an overwhelming one. Relative to more common scenarios that coaches often screw up – like punting on 4th and 1 near midfield – the decision to attempt a late-game conversion appears to be a minor one.

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Extra points:

-Some readers may have identified that the recent increase in extra point distance should be part of the discussion. That may be true. However, while it’s now more likely than before that the leading team misses an extra point that would give it an eight-point lead, it’s also more likely that the trailing team misses a game-tying chance if it were to score when down seven.

-I’ve seen frequent suggestions that teams should vary their decisions based on the caliber of their defense. As one example:

This is fair, but two things to keep in mind. First, when a strong defensive team like Denver goes for two, the benefit of the two-possession lead looms even larger! No way the Chiefs score on two drives last night.

Second, team strength probably doesn’t matter as much as you think. As part of work I did last year for SI.com, I looked at both the game’s point spread and team offensive and defensive efficiency metrics from Football Outsiders as it related to two-point success. While the game’s point spread was a significant predictor (favored teams converted more often), neither the offensive team’s strength alone, nor the defensive team’s strength alone, factored into two-point success. Team-specific probabilities of successful conversions were almost always between 40 and 60 percent, with most of those differences accounted by the game’s point spread.

-I split game minute into two categories above: 0-4 minutes left and 4-8 minutes left. I tried similar splits and they told a similar story.

-It’s worth noting that simply splitting games by deficit alone would be troublesome if there were differences in the team strength among those leading by 7, 8, or 9 points (e.g., if the Patriots and Seahawks always led by 9 points). Judging by the game’s point spread, however, this didn’t seem to be the case. The teams leading late by 7, 8, and 9 points were relatively similar in terms of team strength.

-Extra extra point:

 

 

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