Quarterback Interceptions

by Denis O'Regan

This is an attempt to attach a fairer number to a quarterback's interception rate. Raw interception numbers are naturally improved by taking into account the number of passing attempts a player makes in throwing those picks. However, this still does not differentiate between players who are being asked to throw deeper more often,thus increasing the risk of being picked off. I therefore decided to use play by play data to measure the distance each quarterback's throws travel in the air and divided this by his number of interceptions thrown.I'll call the resulting number airyards per pick. I did this no only for completions, but also for non completed passes.

I've initially just looked at the previous five seasons and I've analysed the quarteback who threw the most passes for each team during each season.As a comparison I've ranked each player for airyards per pick and also for the conventional interception per pass attempt percentage.

Results.

David Carr was the QB I had in mind when I did this comparison. In 2006 he was in his last season at Houston.He was intercepted 12 times from 442 passing attempts giving him a conventional interception % of 2.7% and that was enough to ranking him a more than respectable 13th out of 32 in this stat for QBs that year. If by contrast you look at his airyards per interception, we see a very different story. He threw about 2500 air yards on both completed and non completed passes and if we divide that by his 12 interceptions we find that he threw a pick around once every 200 air yards. Under those ranking conditions he falls almost to the bottom of the pile at 29th out of 32 QBs that year.

On the opposite side of the coin we find that Dan Orlovsky's 2008 season as the major starter of five in Detroit saw him ranked lowly 28 out of 32 in conventional inteception %, but he leaps to a mid table 16th if you account for how frequently he was being asked to air the ball deep. He threw for over 2500 airyards and was intercepted once every 325 yards.

To confirm the different passing styles of each team, the 2006 Texans threw deep just over 10% of the time, perferring to dink and dunk, whereas the 2008 Lions went deep over 20% of the time.

I'll resist the temptation to give a complete list of every QB from 2006 onwards and instead record the players where the conventional stat is most at odds with my air yards per interception stat. Each ranking listed below is for the relevant season and so is out of 32, the higher the ranking the better the player is at avoiding throwing picks.

List of players underrated by conventional interception% ranking

Player	Year	Air Yards Ranking	INT% Ranking
Dan Orlovsky	2008	16	28
Jake Delhomme	2008	15	24
Tony Romo	2006	16	25
Michael Vick	2006	10	18
Matt Hasselbeck	2006	20	27
Vince Young	2006	14	21
Eli Manning	2009	12	18
Rex Grossman	2007	11	17
Ryan Fitzpatrick	2010	18	24
Tarvaris Jackson	2007	24	30
David Garrard	2006	18	23
Derek Anderson	2010	13	18
Jay Cutler	2008	20	25
Jay Cutler	2010	21	26
Kerry Collins	2010	16	21
Kyle Boller	2007	18	23
Tyler Thigpen	2008	21	26

List of players overrated by conventional interception% ranking.

Player	Year	Air Yards Ranking	INT% Ranking
David Carr	2006	29	13
Matt Schaub	2008	29	18
Kurt Warner	2008	22	12
Trent Edwards	2008	30	20
Chad Pennington	2007	29	20
Jimmy Clausen	2010	26	17
Chad Pennington	2006	25	17
Alex Smith	2010	27	20
Bruce Gradkowski	2006	19	12
Sam Bradford	2010	19	12
Trent Edwards	2007	22	15
Matt Cassel	2008	14	8
Shaun Hill	2010	22	16

The method is most interesting when it highlights QBs who have benefited or suffered from the type of throws they are being asked to make, at the extremes of either very good or very bad, both methods tend to converge. Damon Huard's one intereption in 244 attempts in 2006 is the best performance in both methods over the period looked at. He threw an interception every 2,000 air yards. And Josh Freeman's 2009 effort is the worst, again under both regimes.He threw a pick every 150 air yards.