Monday, January 3, 2011

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.


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

PlayerYearAir Yards RankingINT% 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.

PlayerYearAir Yards RankingINT% 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.


dave said...

I took a quick look at two seasons worth of data and int's appeared to be a little over 4 times more likely on deep attempts vs short attempts.

Short attempts were intercepted roughly 1.8% of the time.

Deep attempts were intercepted roughly 8.5% of the time.

Jim Glass said...

Hi, thanks, this was interesting. It got me to look at yards-per-int as a separate stat. Of course picks are included in passing rating, AYA, etc, but the simple yards-per-pick measure I don't remember ever seeing anywhere.

And a very quick eyeballing of the 2010 numbers makes it look like simple yards-per-pick actually has a higher correlation with winning than does AYA: yards-per-attempt adjusted for picks and sacks. That's a very superficial look so I wouldn't bet on it holding up -- but it's interesting that so much less could be more, or even close to it.

The 2010 team numbers are interesting too. Looking at the teams #2 thru #31 the median yds/pick is 213 (Dallas), the low is 109 (Carolina) and the top at #2 is 560 (Tampa) which is a huge gap over #3 at 400 (Pittsburgh).

But the #1 Patriots are in their own universe at 769 yards per pick. In a league where the average for everybody but for them is 245, they are 209 over the #2 team and 369(!) over the #3 team.

denis said...

Thanks for the figures,Dave.
That illustrates why conventional interception rates are so misleading.
Sam Bradford ranks 12th out of 32 in conventional interception%,but he's only been asked to throw deep just over 10% of the time.
He's ranked a lowly 19th when you allow for the air yards he's being asked to throw and that's probably the direction his conventional int rate will head next season if he's asked to go deeper more often.


denis said...

Interesting ideas,Jim
I've always thought that total yards per turnover would be worth a look as well.
I've just finished the best QBs for air yards per interception since 2006 with at least two full seasons as the starter.
Top ten with the best first are Garcia,Brady, Rodgers,Vick,Collins,McNabb,Rivers,Flacco Manning(P) and Orton.
Orton's ranked 5th using conventional interception rates and Vick's ranked 13th,so they are the two big movers in the top ten.

Top ten teams are Phily,Nwe,SD,Indy,GB,Atl,Jax, Balt,TB, and KC.
Both Philly and Nwe throw around 450 air yards per interception and are about 80yards ahead of the 3rd ranked Chargers.
The Jets throw a pick every time the ball's travelled 220 yards in the air and prop up the standings.

Go Dores! said...

Thank you for confirming what I already knew. Jay Cutler: greatest QB EVER.

Jim Glass said...

I'll add the thought that it's not often these days that you see "David Carr" as the top name on any list of the "most overrated".

Notque said...

What is the interception rate on average at Short is 5 yards or less, Mid is 6-15, Deep is 16-25, and Bomb is 26+?

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