Outside of player injuries, penalties may be the most exasperating part of football. While punishing a team for breaking the rules is an important part of ensuring fair play, the arbitrary enforcement1 of what are often vaguely written2 laws can have an outsized effect on the outcome of a football game. And among the penalties that have the potential to impact the game the most, defensive pass interference (DPI) tops the list.
So far this season, there have been 221 DPI penalties called. The interference penalties have been expensive for defenses and massively beneficial for offenses. This season, DPI flags have cost offending defenses 1.42 expected points added per play and bled off a full 4 percentage points of win probability, on average. For comparison, play-action passes (the most valuable commonly occurring offensive play call) this year are worth just 0.25 EPA per play on average — 17.6 percent of the value of a typical DPI call.
DPI is so devastating because, unlike other penalties, the maximum yardage that can be imposed is limited only by the amount of field left between the offense and the end zone. No other penalty can claim the ability to punish a team 99 yards — effectively the entire football field. It’s a special little privilege set aside just for DPI.
While we often view these penalties from the point of view of a defense, ultimately it’s the offense that benefits. And those offenses have a vote as well: Teams can influence the relative value of the DPI calls they receive by choosing when and how deep to throw downfield against a defense. It turns out that the volume of DPI calls a team draws is not evenly distributed across the league. Through Week 13, the New York Giants offense has averaged one DPI call per game, while the Kansas City Chiefs have seen just a single interference flag in their favor.
|New York Giants||13||9.0||12.7||0.98|
|Green Bay Packers||12||14.0||14.8||1.23|
|New England Patriots||11||13.1||9.3||0.85|
|Las Vegas Raiders||10||25.1||20.4||2.04|
|Los Angeles Chargers||9||13.1||13.9||1.54|
|New York Jets||9||26.7||14.9||1.66|
|Tampa Bay Buccaneers||8||17.8||11.2||1.40|
|Washington Football Team||8||20.9||10.3||1.29|
|San Francisco 49ers||5||15.4||6.9||1.38|
|Los Angeles Rams||4||13.3||4.1||1.03|
|New Orleans Saints||2||16.5||2.4||1.20|
|Kansas City Chiefs||1||24.0||1.2||1.20|
The spread in value derived from DPI is even wider: The Las Vegas Raiders have been awarded 20.4 total EPA over the course of the year, while the Chiefs have accrued a measly 1.2 EPA off their lone interference call. Meanwhile, despite being prolific beneficiaries of interference flags, the Giants’ calls have come mostly on shorter passes, limiting their value. New York’s average depth of target on DPI is the second lowest in the league (9.0), ahead of only the Atlanta Falcons (8.2). The distance the ball travels has a sizable impact on the potential value of a DPI call (down and field position are also factors in EPA), so it’s unsurprising that the Giants’ EPA per play is also second lowest in the league (0.98).
The relationship between depth of target and DPI value isn’t perfect, but it helps to explain things at the top end of EPA per play as well. Of the offenses with double-digit DPI calls in their favor, the two teams with the highest aDOT — the Raiders and the Indianapolis Colts — have the highest EPA per play.
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The Colts and Raiders help illustrate another feature of DPI as well: DPI can end up rewarding teams for poor passes. While the bulk of pass interference calls involve a defender impeding a receiver in a way that causes the ball to sail past their position, an important fraction are flags thrown on underthrown passes when the defense was otherwise solid. On such plays, because the ball is short of the mark and the receiver stops his route to attempt to catch it, defenders sometimes fall victim to their momentum and inadvertently run into the receiver, drawing the penalty. And on passes 20 yards deep or greater, no QBs in the NFL have benefited from this particular type of DPI more than Carson Wentz and Derek Carr. According to our charting, Wentz leads the league with five underthrown passes that were bailed out by a DPI call, and Carr is tied for second with three.3
Perhaps there’s an argument to be made that it’s smart to underthrow the ball when a defender’s back is turned in the hope of earning a flag, and in doing so, a QB is displaying a skill. If so, we might expect a great QB like Aaron Rodgers to actively exploit it. However, despite being second in the league in DPI calls with 12, the Green Bay Packers and Rodgers didn’t rely on underthrown passes to earn their flags. Most of Rodgers’s DPI calls came on well-placed passes where the defender impeded the receiver’s ability to catch the ball, and just two came on underthrown passes. But on video, Wentz’s pass attempts don’t appear to be the manifestation of skill. They look like bad throws.
We noted last week that the Colts have been the beneficiaries of good fortune on turnovers so far in 2021, so perhaps this is another example of them running absolutely pure. Indianapolis’s point margin on the season is plus-88, and its EPA on DPIs is 16.5, good for 18.8 percent of its point differential — and half of those flags came on arguably poor, underthrown passes. The question is: Can the Colts’ luck hold? Football is fickle, but between fumbles and fouls, the fates appear to be in Indianapolis’s favor this year.
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