Seven and a half years ago, I asked the question, why do teams run the ball? Today, I want to revisit that post, given that a lot has happened over the last seven and a half years.

Let’s begin my analyzing league-wide pass and rush efficiency. To measure rush efficiency, we will use Adjusted Yards per Carry, which is calculated as follows:

(Rush Yards + 11 * Rush TDs + 9 * Rush First Downs) / (Rushes)

For passing, we will use a modified version of ANY/A by also giving credit for first downs. Here’s the formula:

(Gross Pass Yards – SackYardsLost + 11 * Pass TDs + 9 * Pass First Downs – 45 * INTs) / (Pass Attempts + Sacks)

As a reminder, because touchdowns are recorded as first downs, this formula gives us our familiar 20-yard bonus per touchdown.  Ideally, we would incorporate fumble data into this as well, but unfortunately, we can’t determine whether fumbles happened on rushing plays or pass plays when looking at individual or team game logs. ^[1]Although it does appear that fumbles happen slightly more often on passing plays. As a result, they are ignored in this analysis, but otherwise, this is a pretty good way to encompass the risks and rewards of passing and rushing. ^[2]Also ignored: penalties, but that’s something I’d like to address in a future post.

Now, let’s take a look at the league-wide pass efficiency and rush efficiency rates since 1950.  In black, I have plotted the adjusted yardage gain (using the formula above) for the average NFL pass, while in red, we have the same for each NFL run.  In purple, I have plotted the average AFL pass gain, and used orange for the average AFL rushing gain.  As you can see, there was a time, as recently as the late ’70s, where rushing was more efficient than passing.  But that time has long gone.

To the extent you hear coaches say that running and stopping the run are the keys to victory, know that they are not crazy, just outdated. ^[3]Well, I suppose the two ideas aren’t mutually exclusive. Rushing used to be the most efficient way to move the ball, along with the most consistent. While a higher variance could be the reason teams chose to run instead of pass, that argument holds much less water when passing reaches the efficiency levels present in the modern game.

Which gets us to the next question: how often are teams deciding to pass rather than run? In black, I have plotted the average pass ratio (that is, pass attempts plus sacks divided by total plays) in the NFL for each year since 1950, while in purple, we have the same information for each AFL season. After the 1978 rules changes, the pass ratio in the NFL spiked, and it has been consistently increasing for the last 30 years.

Now, here’s the big question: are teams passing more because they are better at passing? That would make sense, but what does the data imply? I’ve taken the information from the first two graphs to create one last chart. As in the above chart, in black, I have plotted the average pass ratio in the NFL for each year since 1950. This is identical to what you just saw. But now, in red, and against the right Y-Axis, I have plotted the difference between the pass efficiency and rush efficiency averages in the NFL for each year.

That’s remarkable, at least to me. The frequency with which the league passes is nearly directly tied to the delta between pass and rush efficiency. While that makes perfect sense, seeing it in graph form is pretty striking. There are some outliers, of course. In the early ’50s, teams were passing way too much, which perhaps explains why the league seemed to suddenly stop passing in 1956. And from ’99 to ’02, teams may have been passing too much then, too, perhaps unaware that rushing efficiency had increased significantly over the previous decade.

But right now, the two lines are pretty well aligned, which leads to an interesting conclusion. If we re-run these numbers in 7.5 years, and pass efficiency continues to rise, that should mean the historically high pass ratio we currently see should only increase. How long until we finally reach a league-wide 60% passing rate?