I've been chronicling the imbalance in the payoffs of runs and passes on first down in several recent articles. One of the possible explanations for the imbalance is that coaches are too slow to adapt to the NFL rules that seem to become friendlier to the pass year after year. If so, maybe the adaptation to the new realities can be seen in a decrease in the payoff imbalance over recent years.
The graph below charts the difference in payoffs between passes and runs by year. As with my previous posts, data are limited to 'normal' football situations--when the score is close and when time is not yet a factor. As you can see, there may be a slight decreasing trend in the imbalance, suggesting coaches might be catching up.
There's not enough data to say for sure. Obviously, there is some random fluctuation involved from year to year. The NFL's rules keep changing, even through the current season. Plus, the Wildcat offense has created an entirely new wrinkle.
If any apparent decrease in EPA imbalance is real, I'd expect that it's probably due to an increase in the frequency of passing and an according response by defenses. But as we see below, that's not the case. Offenses are passing no more frequently now than in previous years.
An alternate explanation would be that defenses have been adapting, not offenses. Perhaps they have become keyed more towards stopping passes on first down. There's no way to know without better defensive data, so this is just thinking out loud for now.