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Yellow Card: Defensive Pass Interference

May 28, 2012

Yellow Card is a recurring feature about penalties in sports. Today, I discuss the defensive pass interference in American Football.

I mentioned Buddy Ryan’s “Polish Goal-line” formation in a previous Yellow Card article, but I’d like to mention it again because it’s absolutely a perfect example of how penalties aren’t “breaking the rules” as we normally think of it. Because penalties become codified in the rule-set, they actually become just another rule to optimize. If the gain from breaking the rules is less than the cost of the penalty (using expected values, that is, on average), then you’re going to break the rules every time. It’s the rational thing to do to help you win games. Doing so may be a breach of sportsmanship, breaking the “spirit of the game but as The Baseball Codes illustrated, the rules as understood by the players may be different from the rules as understood by the relatively naive audience. When there are million dollar franchises on the line, the “spirit of the game” can quickly become a lesser priority.

So, we need to make a list of all the things we really, seriously, don’t want players to do, and make an appropriate penalty for those actions. Then, we want to identify a list of things that we just want players to think really hard about doing in order to decide if it’s worth it. For those kinds of violations, we design the penalties accordingly. The NFL’s pass interference rules are a perfect example of the latter kind of rule.

According to the NFL rules digest, the penalty for pass interference is defined as follows:

There shall be no interference with a forward pass thrown from behind the line. The restriction for the passing team starts with the snap.

The restriction on the defensive team starts when the ball leaves the passer’s hand. Both restrictions end when the ball is touched by anyone.The penalty for defensive pass interference is an automatic first down at the spot of the foul.

If interference is in the end zone, it is first down for the offense on the defense’s 1-yard line. If previous spot was inside the defense’s 1-yard line, penalty is half the distance to the goal line.The penalty for offensive pass interference is 10 yards from the previous spot.

There’s a lot more that details exactly what constitutes interference, but we’re not really concerned with that right now. I just want to look at how the penalty impacts the player’s decision making process.

On defense, the penalty incurred by pass interference is an automatic first down at the spot of the foul. Generally speaking, that’s a pretty major penalty, and one your certainly don’t want to be committing with any regularity. This makes sense, because the purpose of this rule is essentially to keep the passing game viable and interesting. Fans love big passes. They’re good television: the ball hanging in the air makes for some great moments of cheap drama, and they have the potential to make almost every position on the field a scoring threat, which means that more games are competitive until the final moments.

So, the defensive pass interference penalty basically says “you got in the way, so let’s just assume that he caught it.” In most cases, that’s a sufficient deterrent to the players interfering. In most cases, the defensive player is going to take his chances with a clean catch and a tackle. If you can make the tackle, you get the exact same outcome, but also get the very real possibility of an incomplete pass. With league completion percentages in the 60s, that may not be a bad chance to take.

But that’s not quite the whole story either. Because the ball is called dead at the site of the foul, there’s no chance for the receiver to run for additional yards. So, you’re also trading a guaranteed catch with the penalty for a chance for dropping with a chance for additional yardage. Maybe the cornerback’s taken a beating and isn’t running 100%, and knows the receiver can blow by him or break the tackle. Maybe it’s a cold, wet day, or the receiver’s caught a mysterious case of stupid-fingers the whole game. Taking the penalty may or may not be the best call.

So, there’s a sort of a loophole in the pass interference rules. And there’s yet another consideration when you take the game clock into account. There are some intersections with other rules, such as the fact that a game can’t end on a defensive penalty. If it’s the last play of the game, and the defensive player thinks he’s going to give up the game winning points, he needs to make a call: are the odds of this completion higher than the odds of scoring with the resulting field position? They only get one more play, so it’s a pretty simple calculus. If you’re fielding a strong defense, and simply lost the guessing game at the play call level, what’s to be lost by resetting and trying again? It’s probably not useful to walk this back more than a play or two at a time, but in theory, every play of the game has a similar calculus for the expected value of committing the penalty.

Further complicating matters, we realize that the penalty is based on a judgement call and being noticed by the referee, so the above decisions aren’t simply binary ones. The player simultaneously has to temper his actions based on how likely he is to be caught. In some situations, a flagrant foul with the intent to stop play is indicated. In others, the decision is more complicated. Because the penalty is often no worse than the worst case scenario (and sometimes better), on most plays, the players should do everything just up to the penalty being called. Only in very specific circumstances when a penalty is absolutely undesirable should the defensive player play coverage conservatively.

This is basic strategy stuff, but that’s kind of the point. Basic football strategy dictates that there are times when you willingly “break” the rules. But you aren’t breaking the rules at all, you’re simply choosing a trade-off between an athletic outcome and an officiated one, like calling for a fair catch. By defining the pass interference penalty in terms of the default successful outcome, rather than an arbitrary yardage penalty, the rules create a rich decision point for rational players. And so it’s a perfect example of how penalties shouldn’t be considered breaking rules, but rather just another mechanic to integrate into the players’ experience.


From → Features, Yellow Card

One Comment
  1. Okcrow permalink

    What % of pass plays involve defensive pass interference? Must be pretty low.

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