I've recently been studying YAC and it's complement, Air Yards--the yards a pass travels through the air prior to the catch. So far we've learned that Air Yards are more critical than YAC in terms of generating high yards per attempt stats. We've also learned that YAC should be credited to the receiver only. No matter how accurate a passer is, he does not contribute to his receivers' YAC by hitting them in stride or by other means.
In this post I take a look at the top 30 QBs of 2006 in terms of Air Yards and YAC. Basically, I wanted to find out who the truly good QBs are, and who are the QBs who may appear good because they benefit disproportionately from receiver YAC.
The measures I use for each QB are YAC per Completion and Air Yards per Completion. These two stats tell us how each passer achieved his total passing yards. I also look at completion percentage, which is critical to both YAC and Air Yards--there can be neither without a completion. Applying completion percentage to Air Yards per Completion tells us Air Yards per Attempt.
Air Yards per Attempt captures the essence of passing. It tells us how well a QB throws down field and how accurate he is. It also filters out the effect of receiver YAC, yielding a truer measure of passing performance. Some quarterbacks are able to amass large amounts of yards by throwing short high-percentage passes to backs and receivers who generate big YAC yardage. This inflates the QB's stats above his true talent and achievement.
The table below lists 2006's top 30 QBs in total passing yards. They are sorted in order of Air Yards (AY) per Attempt.
Take a look at the QBs who are living off of YAC--Favre, Brunell, and Carr. Farve is seriously past his prime. Not only is his completion percentage down at 56%, but he's throwing short passes. Brunell was only slightly better, but he has given way to Jason Campbell in Washington. David Carr was by far the king of the dink and dunk passing game. Despite his 68% completion rate, he threw it down field an average of only 4.0 yards on each completion.
The real down-field threats are Romo (5.5), Manning (5.4), and Palmer (4.8). After those three, there is a drop off and a pack of QBs between 4.4 and 4.0 Air Yds/Att. Rivers looks like a solid talent.
Notice how far down the list Brady is. He was throwing a lot of short passes to Dillon and Maroney. Passes to RBs tend to have little or no (or negative) air yards and lots of YAC. He still had solidly above average TD per Att rate and a below average Int per Att rate.
I could go on. There are any number of observations that could be made. It's still not a perfect measure of passing ability, because passing always depends on receivers' abilities to get open and catch the ball. But I believe it is a far better measure than crediting YAC to the QB.