NFL Passing Inflation Since 1977
It is a well-established fact that generalpassing statistics have been on the rise in the NFL over the last 4 decades. While there is little debate over what caused the initial spike in the late 1970s (shorter receiver contact zones and altered blocking rules), there has been significantly mixed opinion on the more recent causes. A common view held predominately by fans is that offense-friendly rule changes and enforcement have given an advantage to QBs and receivers resulting in gaudy increases in passing statistics.
At the same time, there is a smaller camp of writers and analysts that believes the increase in the passing game has been less a result of rule changes, and more a result of less controversial changes in the game like better player develop, smarter schemes, and more aggressive play calling.
But what do the statistics say? How much have passing statistics actually increased and for what reasons?
To uncover the reality, we will compare indexes for a variety of offensive statistics. All data is taken from pro-football-reference.com. Data is for the league as a whole by season and is adjusted for number of teams and number of games played, such that the totals of any season with fewer than 32 teams or 16 games played is pro rated for a like comparison. All figures are indexed to either the 1977 or 1981 seasons.
Since 1977, when the league allowed offensive lineman to extend arms when blocking and lowered the contact zone on receivers from 10 yards to 5 yards, total yards are up 21%, scoring is up 32%, passer ratings are up 45%, and passing yards are up an astounding 63%.
However, more interestingly, almost all of these increases were realized within the first 3 seasons after these two new rules were introduced. Since 1981, total yards are up 7%, scoring is up 11%, passer ratings are up 17%, and passing yards are up just 18%.
These statistics certainly highlight and confirm the positive impact of 1977 rule changes on passing and offense, while at the same time, lend credence to the hypothesis that the impact of rule changes in more recent years is being exaggerated by players and fans. This conclusion is further compounded when examining growth rates over several time periods.
Since 2005, passing yards have increased by an uncompounded annual growth rate of 1.95%. While this is nearly 4 times as fast as the historical average yearly increase since 1980 (0.48%), it is only slightly faster than the growth rate since 1977 (1.85%) and is significantly slower than the annual rates from previous period of rapid expansion like 1992 to 1995 (5.89%) and 1977 to 1981 (14.67%). While recent increases in passing totals may be topical, they are certainly not unprecedented or even that remarkable.
Perhaps we can say that both camps are correct and that while rule changes have had an impact on offenses, they are not the only positive factor. But is there yet another explanation for what has been occurring in the NFL?
We believe that two largely unconsidered statistics shed a deeper light on the evolution of offense in the NFL and historic increases in passing numbers.
In general, QBs are judged by the passer rating which is comprised of 4 components, Yards per attempt, TDs per attempt, completions per attempt and interceptions per attempt.
Yards per attempt, TDs per attempt, and completions per attempt have all stayed within 10% of their 1981 levels, while interceptions per attempt have decreased a staggering 42%. Instead of passing offenses becoming more aggressive as some have purported, it would seem that passing attacks in the NFL have actually become significantly more conservative. This is further emphasized when looking at yards per completion versus yards per attempt.
From 1980 to 1998, yards per completion and yards per attempt generally moved together, however recently there has been a dislocation between these two statistics.
The spread between the two has moved from less than 10 points in 1998 to nearly 20 points today. Logically, if passing attacks had in fact become more aggressive, yards per completion should have increased by a greater factor than yards per pass as more aggressive passing plays gained larger chunks of yardage. To the contrary, it seems that passes have actually become shorter and more conservative. Counterintuitively, attempting shorter passes results in more yards per pass as the increase in completions per pass outweighs the decline in yards per completion.
Ultimately, the increases for overall QB play is the end result of 3 long building trends:
- High percentage, short passing schemes - In the 80s, Bill Walsh and the 49ers introduced the short passing West Coast offense to the NFL, which resulted in a dramatic increase to the team's passing efficiency. As the offensive strategy spread across the league, it brought bigger and better passing numbers to every team that adopted it. More recent evolutions to the WCO, specifically the Patriots' Shot-Gun Spread, have put even more emphasis on the high percentage pass with the predominance of bubble screens and slot drags throughout the playbook. The consequence of such an efficient offense has been higher completion percentages and fewer turnovers, resulting in less reliance on the run which has been traditionally viewed as the most conservative and safest way to move the football.
- Player Development - Some argue that offensive players have become bigger and faster, resulting in an advantage over the defense, but this theory completely discounts physical changes on the other side of the ball. For every receiver who is 20 pounds heavier and 5 steps faster, there is a corner back who is 2 inches taller and multiples more physical. Physiological changes have occurred on both offense and defense. The real change that has affected passing numbers is the mental and mechanical aspects of players. As defenders are reactionary, the offense dictates play not with physical dominance, but rather strategic execution. From a young age, the recent generation of offensive players have been taught to read defenses and adjust accordingly. At the highest levels, this translates to indefensible sight reads designed to deliberately attack a defense where it is has a glaring and obvious weakness. Furthermore, throwing mechanics are being emphasized at younger ages. Margin of error on passes measured in inches rather than feet is becoming less special and more expected, which has in turn allowed new age QBs to take advantage of the developments in scheme mentioned above.
- Rules - While the impact of rule changes has been slightly exaggerated, it is real none the less. As a hermit crab shapes its form to best take advantage of the shells at its disposal, so does an NFL offense shift its philosophy to best take advantage of the rules under which the defense must operate. It is not a coincidence that longer drop backs developed with offensive friendly blocking rules or that 5 yard passes developed with shorter receiver-defender contact areas. Today, greater enforcement of helmet to helmet hits has allowed for smaller and faster receivers to run freer across the faces of much larger LBs. The 5 yard slant is no longer just effective--it is dominant.
The new QB era is undeniable, but ultimately, it should not alter how we view the game of football. As schemes have become more efficient and rules more favorable, the game has not become any easier or softer, just more obvious. At the end of the day, execution, dedication, and unwavering toughness still rule the day.