Adjusted Interceptions 2015

by Vince Verhei

Around this time every year, we look at adjusted interception numbers from the prior season to determine which quarterbacks were actually skilled at avoiding turnovers, and which were merely the beneficiaries of good fortune (and defensive backs with bad hands). Usually we find several quarterbacks whose raw interception totals differ dramatically from their adjusted numbers, and those are the quarterbacks whose story we tell in this space. But there weren't any quarterbacks like that last year. In 2015, every quarterback threw about as many interceptions as he should have.

Before we get into the math, let's explain again how we arrive at our adjusted interception statistics:

• We start with each player's actual interception total.
• 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.
• Next, we subtract plays where the interception (or a dropped interception) was tipped to the defender by a receiver who should have caught the pass. These are listed as "Tip INT" and "Tip AND Drop INT" in the table.
• Finally, we subtract Hail Mary interceptions as well as interceptions thrown in desperation on fourth down in the final 2:00 of a game. These are listed as "HM/End Q4" in the table. In some cases we have included some other late-game fourth-down throws that fell just outside the two-minute mark, but there were none of those in 2015.

Almost all quarterbacks end up with more adjusted interceptions than actual interceptions. Only 23 of the 322 quarterback-seasons with at least 200 passes in the past nine years have had their interceptions adjusted downwards. The biggest disparity on record belongs to Jon Kitna, who threw 12 interceptions with the Cowboys in 2010, including four balls that bounced off his receivers' hands, leaving him with eight adjusted interceptions. The benchmark at the other end of the spectrum was set that same year, when Jets quarterback Mark Sanchez threw 28 interceptable passes, only to see defenders drop more (15) than they caught (13).

There's a slight flaw in that methodology, though, because we know that some interceptions will always be dropped (or broken up by a receiver). Thus, we can't look at a player's adjusted interceptions and say that is the number of picks he "should have" thrown. Instead, we need to take those adjusted interceptions and estimate how many should have been caught. Since 2007, there have been 4,306 actual interceptions in the regular season, and 5,442 adjusted interceptions. That's a ratio of about 79 percent -- in other words, a player's interception total will usually come out to about 79 percent of his adjusted interception total. We can then compare each quarterback's actual interception numbers to his expected interceptions to measure his luck (or lack thereof).

Take Jacksonville's Blake Bortles, for example. The second-year quarterback officially threw a league-high 18 interceptions last season. That includes one pass that hit a receiver first before being tipped to a defender. He threw nine other passes that were dropped by defenders. All of that gives us a total of (18 + 9 - 1) 26 adjusted interceptions, which was also the most in the league. We then take 79 percent of Bortles' adjusted interceptions and credit him with 20.5 expected interceptions. Since he actually threw 18, we can then say that he threw 2.5 fewer interceptions than he should have last year, based on average luck.

That minus-2.5 differential would make Bortles one of the luckiest quarterbacks of 2015, but not the luckiest. That honor would go to Carson Palmer, who threw only 11 interceptions despite an expected total of 14.2. Seven of his interceptable passes were dropped, and none were marked as Hail Marys or tipped passes. The unluckiest? That's a tie between Brian Hoyer and Blaine Gabbert, who each had seven actual interceptions compared to 4.7 expected. Hoyer had two interceptions on Hail Marys while Gabbert saw three passes bounce off his receivers for turnovers (nobody else had more than one). Between them, Hoyer and Gabbert threw only four dropped/defensed interceptions.

And then there's the matter of the Dallas Cowboys. The quartet of Matt Cassel, Brandon Weeden, Tony Romo, and Kellen Moore combined to throw 22 actual interceptions with only 17.4 expected. That's a collective difference of plus-4.6, far more unlucky than any individual quarterback. However, this brings us to the matter of small sample sizes. Individually, Moore threw six interceptions with only 3.2 expected, a difference of +2.8 that was higher than anyone else in the league, including Gabbert and Hoyer. Moore, though, threw only 110 passes, and falls below the 200-pass minimum we usually use for these kinds of measurements. The way this is being computed, perhaps we should use adjusted or expected interceptions as a minimum threshold, and not total passes. In that case, we would likely also eliminate both Gabbert and Hoyer from consideration. Among full-time starters, the most unlucky quarterback of 2015 was… also a tie. Eli Manning and Sam Bradford both threw 14 actual interceptions, compared to 11.9 expected interceptions. Regardless, for now, we will stick with our usual minimum of 200 passes.

Using this methodology, Sanchez's 2010 season remains the luckiest on record. For bad luck, though, Kitna's 2010 season is replaced by yet another 2010 campaign: Eli Manning threw 25 interceptions that year when he was only expected to throw 19.0. Looking at the 20 seasons since 2007 with the best and worst luck, we see that Manning is one of several quarterbacks to make both lists, including Tom Brady, Matt Ryan, Matthew Stafford, and Josh Freeman. This suggests that we really are measuring nothing but luck here, with wild swings possible from one season to the next.

What you won't find in those tables are any seasons from 2015. The +2.3 differential that made Gabbert and Hoyer the league's most unlucky quarterbacks last year was the lowest league-leading mark on record. (If we did away with minimum passes, Moore's +2.8 mark would also be the lowest.) And while Palmer was the NFL's luckiest quarterback last year at -3.2, he would have finished first in that category in just one other season: 2008, when Tyler Thigpen was the luckiest quarterback at -3.0.

So here they are, the very boring numbers from 2015. Players are sorted by adjusted interceptions.

(EDITOR'S NOTE: This table was mistakenly first published with errors in the pass attempts, interception percentage, and adjusted interception percentage columns. Those errors have been fixed.)

With so little to say about 2015, we do have a chance to look back at some historical trends. Palmer's good fortune last season, for example, was nothing new. The veteran quarterback has finished with fewer interceptions than expected seven times in the past nine seasons now, and all told he has thrown 10.5 fewer interceptions than we would expect based on his adjusted interceptions. That makes him the luckiest quarterback since we started keeping track of these things. He's followed by Andrew Luck and David Garrard (both at -9.0, though Luck comes out as slightly luckier when we add a few decimal points), Joe Flacco (-7.8), and Kyle Orton (-6.4).

Meanwhile, no quarterback has had worse total luck than Drew Brees, whose total of 141 interceptions is 12.2 more than his expected output of 128.8. Brees is followed by Philip Rivers (+10.5), Kitna (+8.6), Eli Manning (+8.1), and Gus Frerotte (+8.0). Compare these totals to the luckiest and unluckiest single seasons we listed earlier, and you'll see there's not that much difference in the numbers between the two tables. This is another sign that we are in fact measuring random chance here, and that it's rare for a player to be especially lucky or unlucky for more than a couple of seasons.

Also, the more adjusted interceptions you throw, the more likely you are to see unusually good or bad luck. Eli Manning, Palmer, Brees, and Rivers are all in the top five in total adjusted interceptions since 2007. Jay Cutler, who is second behind Manning in that category, also shows up on expanded leaderboard in these categories.