Introducing "Air Yards"

If I've proven anything over the past year of analyzing NFL stats, it's that passing is by far the most important part of the game. So let's look at the pass and passing stats in more detail than usual.

The football pass is typically judged by how many yards it produces. Quarterbacks and receivers are judged by the their yardage compiled per game or per season. But there are two distinct components of the pass.

A NEW STAT

One of the components that is often discussed is Yards After Catch (YAC). Although it is not an official NFL stat, it is kept by Stats, Inc., and has become a buzzword when talking about the west coast offense. YAC is the yardage gained by the receiver after catching the ball.

The other component of the pass, the complement of YAC, has never been mentioned to my knowledge. It has no name...until now. The distance forward of the line of scrimmage that the passer throws a complete pass through the air is hereby called Air Yards. It can be expressed in a simple equation:

Pass Yds = Air Yds + Yds after Catch

From 2002 to 2006, NFL teams accumulated an average of 3533 yds per season. Of those passing yards, 2008 yds (57%) came through the air and 1533 (43%) yds came on the ground as YAC.

THE IMPORTANCE OF AIR YARDS

Digging a little deeper, I ran a couple very simple regressions. I estimated Passing Yards per Completion using Air Yds/Completion and then using YAC/Completion. (I couldn't run a single regression using both components because multivariate regression doesn't work when the predictor variables comprise the entirety of the dependent variable).

Air Yds/Completion accounts for 56% of the variance in Yds/Attempt, while YAC/Completion accounts for 20% of the variance. As a proportion of the total variance explained by both variables, Air Yds accounts for 74%, and YAC accounts for the other 26%. Put simply, Air Yards are 3 times as important than YAC in producing total passing efficiency.

Here is one way to interpret these results. Although Air Yds yards comprise 57% of total passing yards, it is far more critical than YAC. YAC is less variable among teams. Air Yards, therefore, is much more of a "difference maker" in determining total passing yards.

In future posts, I'll examine how much QBs contribute to YAC. Air yards are a far more appropriate and accurate measure of a QB's ability than total yards or yards per attempt. We'll also see how QBs vary greatly in their ability to produce air yards. Ultimately, these results will contribute to a better QB rating formula.

[Full Disclosure Note: I've continued to search for previous research into air yards. A couple weeks after posting this article, I came across a post (see #11) in a Chiefs message board from back in 2000. A poster named "Romel" not only listed the very same stat (air yds per att), he also called it "air yards." I'm not sure if he computed it himself or got the info from another source. My research here is completely original, but credit must go to "Romel" or to his source for being the first to coin the term.]