As you may have heard, the L.A. Rams had 5.49 adjusted line yards per carry this season, the most for any offense we have ever recorded. Josh Hermsmeyer, however, thinks that says less about the Rams' offensive line and more about the coaching abilities of Sean McVay. Hermsmeyer took a modified version of ALY and adjusted it for defensive men in the box (which is data we didn't have when ALY was invented) and finds that while this year's Rams were excellent, they were not the best of the last 20 years -- that honor goes to the 2012 49ers, the team with Colin Kaepernick and Frank Gore that lost the Super Bowl to Baltimore.
More notable than Hermsmeyer's results, however, is his process. He finds that the number of defenders in the box doesn't just have an impact on the success or failure of a running play, it appears to be virtually the sole determining variable. It almost doesn't matter who's carrying the ball, who's blocking, or who's making the tackle, only how many bodies the defense has available to clog running lanes:
In fact, if all you know about a running play in the NFL is the approximate field position of a team and the number of defenders near the line of scrimmage, you're able to predict the leaguewide yards per carry with an extraordinarily high degree of accuracy: 96 percent of yards-per-carry totals are explained by the offense's field position and the number of men the opponent has in the box. How many defenders are in the box is almost certainly the most important factor in determining rushing success in football, so it follows that we should try to account for it.