by Vincent Verhei

EDITOR'S NOTE: After publication, we realized our totals for pass attempts for all players had been miscalculated, and as a result player's interception rates were also incorrect. The data table now has been fixed, and the text referencing those errors has been corrected where applicable.

When is an interception not an interception? Typically, when a defender drops a pass that he should have caught, or when a wide receiver makes a big play to turn what should have been a turnover into an incompletion instead. On the other hand, sometimes quarterbacks are charged with interceptions that aren't really their fault -- Hail Mary passes, for example, or those that bounce off a receiver's hands and into a defender's.

After each season, we go back and account for these discrepancies and account for each quarterback's adjusted interceptions. Here's the process:

• We start with each player's actual interception total. DeShone Kizer led the NFL in 2017 with 22 interceptions.
• We then add plays where the quarterback threw a ball that could have or should have been intercepted but was not, either because the defender outright dropped the ball (which we have been tracking in game charting since 2007), or he had it knocked out of his hands by an offensive receiver (a "defensed interception," which we have been tracking since 2012). These are listed as "Drop/Def INT" in the table at the end of this page. Kirk Cousins and Matthew Stafford tied for the league lead with nine such passes each. Aaron Rodgers was the only qualifying passer to not benefit from a dropped interception.
     

• Next, we subtract those interceptions that were tipped by receivers into the hands of defenders. Matt Ryan threw five interceptions that should have been caught by his own teammates. That wasn't just the most in the league, it was the most for any quarterback in a single season since Eli Manning also had five in 2010. We also subtract passes that are tipped by receivers but then dropped by defenders to make sure they are not double-counted. C.J. Beathard, Mitchell Trubisky, and Andy Dalton each had one play like that last season.
• Finally, we subtract Hail Mary interceptions, as well as interceptions thrown in desperation on fourth down in the final two minutes of a game. (We're sometimes flexible on these definitions, but not in 2017 -- there just weren't any gray area interceptions last season.) These are listed as "HM/End Q4" in the table. Kizer and his homonymic peer Deshaun Watson each had two such interceptions last year; nobody else had more than one.

When we started running these numbers, we had to get the data from our own in-house volunteer game charters. For the last three seasons, we've had access to data from Sports Info Solutions. Determining whether or not a defender should be charged with a dropped interception will always be subjective on some plays, but you can rest assured that all the obvious calls have been counted here.

Enough with the minutia -- let's get to the big table of numbers!

After all that work, Kizer still leads the league in adjusted interceptions, but the gap between him and the rest of the league has shrunk considerably. It's certainly not a good thing that Kizer threw 23 adjusted interceptions, but it's hardly unprecedented -- Ben Roethlisberger and Eli Manning both threw more than that last year. Kizer didn't get a lot of help from Lady Luck -- defenders only dropped six of his passes, while five came on either Hail Marys or drops from his receivers. Quarterbacks typically finish with about three-fourths (77 percent, to be more precise) as many actual interceptions as adjusted interceptions. Since Kizer had 23 adjusted interceptions, we would have expected him to throw 17 or 18 actual picks, not the 22 you'll find on his page at NFL.com.

The three quarterbacks who threw 20 or more adjusted interceptions in 2017 will all play for new teams this year. Kizer was traded to Green Bay, while Trevor Siemian and Kirk Cousins both moved to Minnesota, Siemian via trade and Cousins in free agency. Siemian only threw 406 passes last year and actually had the league's highest rate of adjusted interceptions, but then he's going to be a backup for the Vikings, and you'd expect backup quarterbacks to struggle with ball security. Cousins, however, was briefly the highest-paid player in the league by average salary. He has since been passed in that category by Matt Ryan, but that doesn't mean Minnesota's expectations for him have lowered. If his luck comes back to earth, you can expect your Vikings fan friends to be extra grouchy.

If we go by rate of adjusted interceptions instead of totals, we find Siemian first at 4.9 percent 5.2 percent, followed by a pair of Cardinals: Carson Palmer (4.8 percent) and Blaine Gabbert (4.3 percent 4.6 percent). Between Palmer, Gabbert, and Drew Stanton, the Cardinals threw 28 adjusted interceptions, which is why none of the three will be Cardinals in 2018. Kizer, meanwhile, combined with Kevin Hogan and Cody Kessler to throw 31 adjusted interceptions in Cleveland, which is why none of them will be with the Browns in 2018. Instead, Cleveland will (probably) be quarterbacked by Tyrod Taylor, who had the lowest adjusted interception rate in the league, followed by San Francisco's C.J. Beathard and Atlanta's Matt Ryan.

If those last two names are surprising for you, well, that's the whole point of adjusted interceptions. We mentioned Ryan's terrible luck with tipped interceptions last year, and that most quarterbacks end up with significantly more adjusted interceptions than actual interceptions. Well Ryan's luck was so bad that he actually threw three fewer adjusted interceptions than actual interceptions, the first quarterback to do that since Tom Brady in 2013. Beathard was right behind him, with two more actual interceptions (six) than adjusted interceptions (four). And Beathard threw less than half as many passes as Ryan did!

Beathard won't be starting in San Francisco this year, of course; Jimmy Garoppolo will. For all his success last season, Garoppolo threw five interceptions in 188 passes, a higher rate than most quarterbacks. And he had three dropped interceptions for a total of eight adjusted interceptions, a rate of 4.3 percent that would have ranked right behind Siemian, Palmer, and Gabbert among the highest in that category.

Here's a look at adjusted interceptions in prior seasons.

• 2011
• 2012
• 2013
• 2014
• 2015
• 2016

Posted by: Vincent Verhei on 30 May 2018

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