Instant replay review is one of the cornerstones of the modern NFL. The process and its myriad special rules have been internalized and constantly debated. Mike Kurtz wonders: is it worth it?
07 Dec 2012
Guest Column by Keith Goldner
Recently, Pro Football Talk published an article discussing potential plans to eliminate an opening kickoff entirely.
"Sean Gregory of TIME writes that one of the options being considered for replacing kickoffs entails giving the ball to the team that would have been kicking off at its own 30, automatically facing a fourth down and 15 yards to go. The team can then choose to punt or go for it, via fake punt or otherwise.
In other words, the kickoff would be replaced with the punt, and the onside kick would be replaced with a fourth-down conversion roughly half the distance of Ray Rice’s recent catch-and-run."
The idea Roger Goodell is sharing with Gregory actually comes from Tampa Bay head coach Greg Schiano, who first talked about such an idea when he was still head coach at Rutgers. A huge change like this is certainly a long shot, but it's a bit less of one now that the idea has been publicly floated by the commissioner. With that in mind, I decided to run the numbers and see who this new rule would favor. A couple of things to note:
I tried to incorporate as much as possible into the analysis. Here are the probability and frequency breakdowns, with an estimate of expected points (EP).
Based on the adjusted expected points value at the bottom, the punt would result in twice as many expected points as the current kickoff rule (1.15 versus 0.53) for the receiving team. The majority of that comes from the difference in average starting field position. Kickoffs from the 35 have resulted in an average starting field position at the 21.6, whereas punts from around the 30 result in a starting field position at the 30.4-yard line. This also assumes that teams will fake punt/go for it on the fourth-and-15 as frequently as teams attempt onside kicks, be they surprise or not.
The biggest difference other than those mentioned above (all the poor outcomes possible for punts) is the change in the probability of converting a surprise event. Surprise onside kicks convert at an extremely high 60 percent rate -- and should most likely be attempted way more frequently than they currently are. Fake punts from around 15 yards convert at roughly the same rate as a regular fourth-down attempt -- though keep in mind this is just an estimate since this scenario occurs extremely infrequently. The defense has a much better chance to stop a fake punt that has to convert 15 yards (either a 15-yard run or completion) than they do to recover a bouncing ball where the only requirement is for it to travel 10 yards.
The next step would be to look at injuries and the severity of injuries on kickoffs and punts. I'm sure the NFL has researched this and found that the average number (and especially the severity) of injuries is lower on a punt than a kickoff, otherwise this never would have even been mentioned.
One other note is that I would guess teams would begin returning punts more frequently than they currently do, eschewing fair catches. Teams started returning balls from deeper and deeper in the end zone when the kickoff was moved up.
But, when should teams actually go for it on the fourth-and-15 attempt?
First, let's look at expected points. This will tell us how often, in general, teams should attempt the fourth-down conversion. We will use the values from the last post and assume a fake punt and conversion attempt both convert at 20 percent.
EP (Normal Punt) = -1.02
EP (Conversion Success) = 2.23
EP (Conversion Failure) = -3.28
Next, we set up the equation to solve for the break-even conversion rate:
2.23 * x - 3.28 * (1 - x) = -1.02
x = 0.41
So, teams should go for it if they believe they can convert over 41 percent of the time. Since the estimated conversion rate is about half that, teams should very rarely go for it. That does not mean they should never go for it, as there are obvious elements of game theory involved -- success probability would increase as your opponent's belief in you attempting the fourth-down conversion decreases. And, most notably, at the end of the game, we must take win probability into account.
Let's first look at a surprise attempt -- fake punt -- taking place in a tie game nearing the end of the third quarter. Most teams would not be expecting a fake here.
WP (Normal Punt) = 0.45
WP (Fake Success) = 0.59
WP (Fake Failure) = 0.38
Solving the same equation, we get x = 0.33. Closer, but still higher than our estimated conversion rate. This goes against previous analysis of surprise onside kicks.
Regular onside kicks typically happen when there is less than a 15 percent chance of winning the game. Take the following scenario: Your team just scored, and you are down three with three minutes left.
WP (Normal Punt) = 0.12
WP (Conversion Success) = 0.38
WP (Conversion Failure) = 0.06
Here, x = 0.1875 < 0.20, so the team should attempt a conversion rather than just punting. Obviously, timeouts are a factor in this scenario, but generally, the analysis applies.
It will only make sense to attempt the conversion if your team has less than a 15-to-20 percent chance of winning the game. Above, you can see a (very) rough estimate of the break-even points based on the estimated win probability if the team were to punt the ball normally rather than attempt to convert on fourth-and-15. The thick red line represents the estimated conversion rate on fourth-and-15; a team would only be justified by the math to attempt a conversion when the break-even point was at or below the red line.
Keith Goldner is the creator of Drive-By Football, and Chief Analyst at numberFire.com -- The leading fantasy sports analytics platform. Follow him on Twitter @drivebyfootball or check out numberFire on Facebook. Part of this analysis originally appeared on his own site.
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