Onside Kicks
With 4 minutes left in the first quarter of last week's Cardinals-Seahawks game, Arizona's Neil Rackers booted a short but high 'pooch' kick that was quickly recovered by the kicking team. The kick recovery was worth a very considerable +0.12 WP. The Cardinals went on to score a touchdown, taking a 14-0 lead. How smart are onside gambles like this?
Onside kicks in the NFL are successful 26% of the time. It’s true, but it’s also very misleading. Onside kick success rates are very dependent on whether the receiving team is expecting one.
As you can see in the chart below, a plot of the frequency of onside kicks by win probability (WP), teams don’t usually attempt onside kicks unless they’re pretty desperate. Teams typically attempt them when they have less than a 10% chance of winning. Even then, they only do it about 26% of the time.
The effect of surprise on the success of an onside kick is pretty big. The chart below plots success rate by WP. The less a team is expecting an onside kick, the more successful it is. When teams are expecting it, when WP is about 0.15 and below, the success rate is about 20%. But when teams aren’t expecting it, the success rate averages 60%. (There are 103 onside kicks classified as 'surprise' in the data, which results in a standard error of +/- 4.8%.)
What does this mean for surprise onside kicks? Are they worth the risk given a 60% success rate? We can answer that question with an analysis based on Expected Points, the average of next points scored for first downs at each yard line on the field. In the following example, I’ll solve for what the break-even success rate would be for an unexpected onside kick.
The EP for a failed onside attempt is -2.1 pts, and the EP for a success is +1.2 pts. At first glance it appears onside kicks are always losing propositions. But don’t forget that you’ve always got to kickoff somehow, and a normal kickoff averages -0.7 pts for the kicking team.
EP(onside recovery) = +1.2
EP(onside failure) = -2.1
Let’s call the success rate ‘x’. Solving for the break-even success rate, where the combined expected points of an onside kick equal that of a normal kick, we get:
1.2x - 2.1 +2.1x = -0.7
3.3x = 1.4
x = 42.4%
So 60% is a lot more than the break even success rate of 42%, and as long as a team has the element of surprise, onside kicks are well worth the risk—at least under ‘normal’ football conditions. Late in games, however, depending on the score and time remaining, we can’t use the EP analysis anymore. We need to turn to win probability analysis, something I’ll look at in part 2 of this article.
The catch is that teams can’t do this very often. The key is that the onside attempt is unexpected. As soon as a team is known for sneaky onside kicks, its success rate will go down. But this isn’t such a bad thing. As opponents are forced to respect the threat of an onside kick, their normal kick return blocking will suffer, allowing overall net kickoff distance to improve. Ultimately, there would be an equilibrium, making life more difficult for the receiving team.
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11 comments:
This is great work. Its a topic I've thought about a bit and have always wanted to study more deeply.
I'm sure readers of this blog have heard of Pulaski high school in Arkansas. The coach is famous for never punting. He is also famous for trying an onside kick everytime.
The math is somewhat dependent on the fact that high school kickers can't kick as far and opposing teams special teams don't practice covering onside kicks as often as NFL teams do. So the math is not directly comparable to the NFL. Yet its still an interesting story because I think he has the math right and his opponents don't.
I'm especially interested in the game theory and equilibrium issues that would be involved in running a "surprise" onside kick far more often....say around 20% of the time. The biggest difference between a surprise onside and an expected one is the receiving team's personnel. They replace the big blockers with small wide receivers. If a team ran "surprise" onside kicks more often, they could always change the call at the last minute. If hands guys are on the front line, kick away. If not, go through with it.
The other problem from an adjustment point of view is preparation time. Say there is one team that surprise onsides 20% of the time and all the others do it 1% of the time. Clearly, when you are getting ready for that one team, you should prepare for it more often. What does that mean in real life though? Special teams units don't get as much practice time as most of the players have other responsibilities. How much time can you dedicate to a trick play you are likely to see only so often? Also, from one team's perspective, getting another team to spend more time preparing to stop a gadget play has real advantages in the corollary that they spend less time preparing for everything else.
Do you have the stats on onside kicks in the 1st half when it is a surprise?
I notice there is a dip in success rate right at 50%-60% chance of winning. Is this random, or does this represent teams trying an onside kick at the start of the game, where the surprise onside kick may not be as surprising as say, with 4 minutes left in the first quarter?
Do you have the data separated out by kicks at the start of a game/half (when coaches can prep the players coming in on both sides), versus after a score when the kicking team isn't in a very low WP situation?
According to Pro Football Prospectus 2007, "surprise" onside kicks had a 71% success rate from 1996-2006.
Interesting. How was "surprise" defined?
I'm guessing based on the behavior of the receiving team. If they have a deep guy and blockers, they were expecting a regular kickoff. If they are crowding the line, with maybe one guy deep, they were expecting an onsides.
But Pro Football Prospectus probably just used some guy's opinion.
I'm looking at the PFP 2007 article, and I don't see a definition of what makes an onside kick a "surprise." Their numbers are: from 1996-2006, there were 78 surprise onside kicks, 55 of which were successfully recovered (71%), and 516 expected onside kicks, 85 of which were successfully recovered (16.5%). They say that the break-even point for a surprise onside kick is 62% (rather than 42%): successful recovery at your own 40 is worth .94 EP, failure to recover giving the other team the ball at your 40 is worth -2.13 EP, and kicking deep on average gives the other team the ball at their 27.4 which is worth -.24 EP.
That's weird. The difference in the break-even success rate is just due to different EP values. I'm not sure how they derived those, but they are very different from the others I've seen.
Based on Levitt/Kovash EP values:
Success=+1.7, Fail=-2.3, Deep Kick=-0.6
Break even = 43%
Based on Romer EP values:
Success=+1.5, Fail=-2.4, Deep Kick=-0.6
Break even = 46%
Vince-Forgot to say thanks for digging that up.
I think Sean Payton reads your stuff, Brian. He told the media after the super bowl that he thought the chances of recovering that onside kick in the super bowl were around 60%-70%. From most of the stuff I read after that, everyone thought he was full of crap and just really lucky.
Of COURSE, most people "thought he was full of crap and really lucky." That derives from the fact that a large majority of football fans and even real football men are so tradition-bound that they refuse to acknowledge that they refuse to acknowledge the math, even when it whacks them upside the head.
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