By Zach Voget
It’s the same story every time. An NFL team scores a touchdown and barring unusual circumstances, said team earns seven points. With extra-point kicks snapped from the two yard line, kickers rarely miss the 20-yard chip shot. The short field goal provides no incentive for teams to go for two-point conversions, with virtually a 100% chance the team will earn one-point following the touchdown.
This past summer, the NFL changed the length of the one-point conversion to make the decision a little tougher and the game more exciting. Rather than snapping from the two-yard line, teams must snap the extra-point kick from the 15-yard line, making the kick about 33 yards. If the team decides to go for two points, they can still snap the ball from the two yard line and run a play. The question is: will this make enough of a difference to dissuade teams from going for one?
Through Week 3, the rule change can already be noted through some team’s decision making while others seem completely unfazed. For example, the Pittsburgh Steelers seem to have embraced the role of a team willing to go for two on more occasions. They lead the league with four attempted two-point conversions, one less than the number of extra-point field goals they have attempted. On the flipside, the Arizona Cardinals, who have already scored 17 touchdowns, have yet to attempt a two-point conversion and have decided to just take the longer field goals.
So is it worth going for two? How can we determine whether going for two or sticking with the field goal is a better move from an analytical standpoint?
Taking the sample size through Week 3, I determined the league-wide average for one-point field goals and two-point conversions. Through Week 3, teams attempted 239 one-point field goals and have converted 226 of them, a 94.56% clip. This year, teams have attempted 25 two-point conversions and have been successful on 12 of them, a 48% clip.
We can use Expected Value, a common analytical approach in basketball and statistics, to analyze the value of one-point vs. two-point conversions. Expected Value takes an average success rate and multiplies it by the value of that successful outcome, giving you the value you can expect on average for your course of action. Let’s apply this to football. The previously determined success rate one-point field goals is 94.56%, and if we multiply this by the value of the successful outcome (one point), we get an Expected Value of .9456 points (.9456*1) per one-point conversion. We can do the same for two-point conversions, multiplying .048 (48%) by 2 (value of successful outcome), making an Expected Value of .96 points per two-point conversion.
This means that, on average, we can expect to get .15 points more per two-point conversion than one-point conversion, and in a high scoring game could be the difference necessary for victory.
There are some clear limitations to this calculation, one of which belongs a small sample size. As the season progresses, the percentages will start to normalize and this calculation can continue to improve and become more accurate. The other limitation is that it does not account for situational decisions. If a team ties up the game with a touchdown at the end and only needs one point to win, they should not look at the expected points per attempt to decide whether to go for one or two, but rather the conversion rate and kick the field goal. In general though, this calculation shows that if these percentages continue to hold, teams should be going for two more often with the new rule change.
Stats courtesy of Sporting Charts and ESPN