But you rarely see Luck’s completion split into (a) 10 yards through the air, and (b) 15 yards after the catch by his receiver. Brian Burke calls those 10 yards “Air Yards” and I think that is a pretty useful moniker. The question is, what do you do with Air Yards? Luck led the NFL in Air Yards per completed pass last year (8.0), but that doesn’t make the statistic an indicator of quality. Tim Tebow’s 2011 performance produced the highest single-season Air Yards per completion average since 2006 (8.9), while Jake Delhomme (2008) and Derek Anderson (2010) each have led the league in that metric, too. Air Yards per completed pass is a very useful way to describe a player’s style, but you can’t use it alone to determine a player’s quality.
One question I have: Are Air Yards more repeatable for a quarterback than the yards he gains via his receivers’ YAC? It’s important to keep that question separate from this one: Is a quarterback who has a high number of air yards and a low YAC better than a quarterback in the opposite situation? Today, I plan to focus on the first question, but let’s take a second to address the second one.
According to ESPN’s research, yards after the catch is more about what the receiver does than the quarterback. As a result, a completion that is in the air for 40 yards is better for a quarterback’s ESPN QBR than a pass that is in the air for 5 yards on which the receiver runs for 35 yards after the catch. That makes sense, I suppose, and I suspect that’s probably true more often than not. The easiest counterargument is to point to Joe Montana, and say that what made Montana great was his pinpoint accuracy that enabled players like Jerry Rice to rack up big YAC numbers.I’m going to put off any further analysis of how much of YAC should be attributed to the quarterback and how much to the receiver, because it’s pretty complicated. One thing that is a bit easier to analyze is how “sticky” Air Yards are from year to year.
Examining data from the NFL’s Game Statistic and Information System (NFLGSIS), there have been 100 quarterbacks from 2006 to 2012 who threw at least 290 passes for the same team in consecutive years. The correlation coefficient between Air Yards per completed pass in Year N and in Year N+1 was 0.26. You might get a sense that such a relationship is really weak, but if you’re unfamiliar with CCs, let’s look at the same set of 100 quarterbacks and how “sticky” their other metrics are:
- The correlation coefficient between Completion Percentage in Year N and in Year N+1 was 0.51.
- The correlation coefficient between Yards/Attempt in Year N and in Year N+1 was 0.51.
- The correlation coefficient between Touchdown Rate in Year N and in Year N+1 was 0.34.
- The correlation coefficient between Interception Rate in Year N and in Year N+1 was 0.08.
- The correlation coefficient between Air Yards on all passes (i.e., including the distance of the throw on incomplete passes) in Year N and in Year N+1 was 0.34.
- The correlation coefficient between Yards after the Catch in Year N and in Year N+1 was 0.34.
So what does that mean? A high correlation coefficient doesn’t mean the stat is more important, just more predictive. We shouldn’t be surprised to see that completion percentage is consistent from year to year. Completion percentage is not sensitive to outlier plays and is calculated over a very large sample size. Of course, that doesn’t make completion percentage very important, just easy to predict.
On the other hand, it is a little surprising that Air Yards per completed pass isn’t stickier from year to year. Here’s another way to show the lack of year-to-year correlation. I looked at the top 20 and bottom 20 quarterbacks in AY/CP in my 100-sample set. The top 20 quarterbacks averaged 7.9 Air Yards per Completed Pass in Year N and 6.9 AY/CP in Year N+1; the bottom 20 quarterbacks averaged 5.7 AY/CP in Year N and then 6.4 AY/CP in Year N+1. In other words, the gap between the best and worst quarterbacks drops from about 2.2 to 0.5 from year to year. That’s a little counter intuitive to me, as I would think coaching philosophies don’t change much from year to year.
Carson Palmer, 2011-2012, had the biggest dropoff in Air Yards per Completed Pass, dropping from 8.55 in 2011 to 5.97 in 2012. Part of that was due to injuries, but in 2012, TE Brandon Myers and FB Marcel Reece led the team in receptions while deep threat Darrius Heyward-Bey led the team in receptions in 2011. Denarius Moore also saw his yards per reception drop from 18.7 to 14.5, although it’s hard to know whether Palmer was the cause or the effect there. Under Bruce Arians, Andrew Luck led the league in AY/CP in 2012; it will be very interesting to see how Palmer does under Arians’ tutelage in 2013, and if Palmer can regain his 2011 form (which was only over 9 games).
On the other hand, Josh Freeman 2011-2012 saw the biggest increase in AY/CP, jumping from 5.61 in 2011 to 7.92 in 2012. Adding Vincent Jackson (19.2 YPR in 2012) played a big part, and I discussed the impact of offensive coordinator Mike Sullivan for on Freeman back in November. Freeman ranked 3rd to last in AY/CP in 2011 (ahead of only Ryan Fitzpatrick and Blaine Gabbert), which was a gross misuse of his talents. Of course, he was also playing for a Tampa Bay team that mailed it in the final two months of that season.
Interestingly, average YAC has a higher correlation year-to-year than average AY/CP. For that matter, so does Air Yards per Attempt, which includes incomplete passes. That statistic is what Mike Clay calls “average depth of target” or aDOT; I’m not surprised about the latter, as we simply have a larger sample, making the results more reliable in any one year. As for the former, it’s hard to say. The difference isn’t very big and our sample isn’t large, so it could just be random. Initially, I would assume that AY/CP would be stickier than average YAC, but if you were the type of person to argue that good quarterbacks consistently throw accurate passes that enable their receivers to pick up yards after the catch, you’d be happy to see this result.
The best-fit formula to predict future AY/CP in Year N+1 is 5.1 + 0.23*Yr N AY/CP. The number to focus on there is the coefficient of 0.23: this means if one quarterback averages one more AY/CP than another quarterback in Year N, the difference is projected to shrink to just 0.23 AY/CP the next season. For Year N+1 YAC, it’s 3.5 + 0.31*Yr N-1 YAC. So for every one additional yard of YAC in one year, we expect 0.31 additional yards of YAC per completion the next season.
Again, we can’t gain too much insight into a sample of only 100 quarterbacks, but these two formulas do indicate that YAC may be easier to predict for quarterbacks than Air Yards. At least to me, that’s a surprising result.