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DanT · 05-24-2020, 05:43 PM

I don't think the NFL has given enough thought to where the play should begin. The explanation their analysts offer here doesn't mention the expected value of different parts of the field, such as are described here.
According to the NFL's explanation, they estimated the success probabilities of the onside kick and the 4th and 15 play to be 13.2% and 16.8% respectively. But let's incorporate the expected value of the field position to get a rough sense of the expected payoff.
For an onside kick from the 35, whichever team gets the ball is going to be around the 50, where the expected points added (EPA) is about 1.5, so the kicking team that elects to go for an onside kick is looking at a 13.2% chance to win 1.5 EPA versus a 86.8% chance to lose 1.5 EPA, an expected payoff of -1.1 EPA. The negative value is why you don't see teams go for onside kicks very often, of course.

For a 4th and 15 from the 25, let's say that a conversion also puts you around the 50, a generous assumption, so you can get 1.5 expected points. If you fail, though, the opponent will be starting from inside the 40, so has an EPA of at least 2 points, so the expected payoff for the team that decides to go for it would be
(16.8% * 1.5 EPA ) - (83.2% * 2 EPA ) = -1.4 EPA.

So, from an expected payoff standpoint, it's less attractive to go for it with a 4th and 15 than with an onside kick.

Of course, these are just averages and I'm using them in just a very rough way to evaluate whether we might see more attempts from the scoring team to retain possession. My guess is that we definitely won't see more during the first 3 quarters, even though then the probability of success for an onside kick may be a bit higher due to the element of surprise. I wouldn't be surprised if in the 4th quarter, there isn't an overall increase, either. Late in games when teams are desperate, there might be some teams that are more willing to go for it with a 4th and 15 play than they are with an onside kick. I'd be comfortable with Mahomes going for it, because he's the best player I've ever seen. Of course, if your QB is good enough to give you confidence to take a 4th and 15 shot, you're probably not going to be in many desperate late-game situations.

Denver proposed this rule originally and wanted to start from the 35. That may be too far forward, but I think 25 is too far back, if the goal is to increase more attempts to keep the ball after scoring.

05-24-2020, 05:43 PM	#19
DanT Veteran Join Date: Sep 2000 Location: Davis, CA Casino cash: $4501711	I don't think the NFL has given enough thought to where the play should begin. The explanation their analysts offer here doesn't mention the expected value of different parts of the field, such as are described here. According to the NFL's explanation, they estimated the success probabilities of the onside kick and the 4th and 15 play to be 13.2% and 16.8% respectively. But let's incorporate the expected value of the field position to get a rough sense of the expected payoff. For an onside kick from the 35, whichever team gets the ball is going to be around the 50, where the expected points added (EPA) is about 1.5, so the kicking team that elects to go for an onside kick is looking at a 13.2% chance to win 1.5 EPA versus a 86.8% chance to lose 1.5 EPA, an expected payoff of -1.1 EPA. The negative value is why you don't see teams go for onside kicks very often, of course. For a 4th and 15 from the 25, let's say that a conversion also puts you around the 50, a generous assumption, so you can get 1.5 expected points. If you fail, though, the opponent will be starting from inside the 40, so has an EPA of at least 2 points, so the expected payoff for the team that decides to go for it would be (16.8% * 1.5 EPA ) - (83.2% * 2 EPA ) = -1.4 EPA. So, from an expected payoff standpoint, it's less attractive to go for it with a 4th and 15 than with an onside kick. Of course, these are just averages and I'm using them in just a very rough way to evaluate whether we might see more attempts from the scoring team to retain possession. My guess is that we definitely won't see more during the first 3 quarters, even though then the probability of success for an onside kick may be a bit higher due to the element of surprise. I wouldn't be surprised if in the 4th quarter, there isn't an overall increase, either. Late in games when teams are desperate, there might be some teams that are more willing to go for it with a 4th and 15 play than they are with an onside kick. I'd be comfortable with Mahomes going for it, because he's the best player I've ever seen. Of course, if your QB is good enough to give you confidence to take a 4th and 15 shot, you're probably not going to be in many desperate late-game situations. Denver proposed this rule originally and wanted to start from the 35. That may be too far forward, but I think 25 is too far back, if the goal is to increase more attempts to keep the ball after scoring.
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