Recently, I looked at onside kicks using an expected point analysis. We saw that "surprise" onside kicks could give a kicking team a big advantage. The break-even recovery rate would need to be 42% to make one worthwhile, and unexpected onside kicks are currently recovered 60% of the time.
But the expected point analysis only applies to "normal" football game situations. It does not account for the particular situations shaped by score and time remaining. For that we need to turn to win probability (WP).
Let's start with an example. It's the beginning of 4th quarter, and the kicking team has just tied up the game. An onside kick would clearly be unexpected in this situation, so we'll use the 60% recovery rate. A normally deep kick would result in a 0.44 WP. Getting the ball at its own 40 would give the kicking team a 0.56 WP, but a failed onside kick would result in a 0.40 WP.
WP(onside recovery) = 0.57
WP(onside failure) = 0.40
Given the 60% surprise recovery rate:
WP(onside) = 0.50
Further, if we approach the math another way, by setting the WP of the onside kick to equal that of a conventional kick, we can solve for the break-even recovery rate. In this case it would be 25%. A kicking team would need to successfully recover the onside kick only 25% of the time for it to be worthwhile. This rate isn't much higher than the 20% recovery rate for expected onside kicks.
The graph below plots the increase in WP for the onside kick attempt over a normal kickoff. Where the graph is positive, it is better to kick an onside kick, and where it’s negative, it’s better to kick deep.
The graph assumes the following: If the kicking team’s WP is currently 0.15 or below, the probability of onside success is 0.20. But if it’s above 0.15, the onside kick will be a surprise, and the probability of success is 0.60. (This is from what we learned in a previous post.) The x-axis is time left in the game, and the y-axis is the benefit in WP from kicking onside. I’ve selected 3 cases to illustrate, where the kicking team is ahead by 7, tied, and down by 7.
The lines are somewhat noisy, but they do show some very interesting trends. The feature that stands out the most is the large spike at the end of the game for when the score is tied. This is suggesting that a team that is kicking off with just 2-3 minutes remaining is much better off kicking a surprise onside kick. With that much time left, an opponent has plenty of time to score, and if it does, the kicking team would have almost no time to respond. Plus, a successful onside kick could be nearly fatal to the opponent, depending on the number of timeouts available.
Possession of the ball is absolutely critical in this situation. All things considered, the advantage of kicking onside increases the WP of the kicking team by 0.22 from about 0.33 for a standard kick.
As we found with the expected point analysis from the previous post, a surprise onside kick is almost always beneficial. It always depends on the game situation at hand, and time remaining is a critical component.