Stat Your Face Off: ALY (Adjusted Line Yards) Explained

We're a running team. Our (2010) 12th ranked rushing YPG average will tell you that.

We're stout against the run. Our (2010) 10th ranked rushing yards allowed/game average will tell you that.

But alas ... the age-old question: is there more out there to confirm our awesomeness?!?! THERE IS! And it's called ALY.

Join me after the jump for some statistical awesomeness.

ALY tries to separate running back performance from offensive line performance. Not an easy task. Sort of like trying to separate a Falcoholic from his Falcohol.

Here is the Football Outsiders explanation.

Here is the Wikipedia short version:

Adjusted Line Yards (ALY) is a statistic that attempts to measure an offensive line's contribution to the running game, separating the blocking from the runner himself. Each of a team's running plays are included, with yards gained weighted by category -- losses, where a runner is tackled in the backfield, are weighted heavily against an offensive line, while long gains, where a runner is far beyond his initial blocks, are reduced and eventually eliminated. The plays are adjusted for game circumstances, and the result is normalized so that the league-average ALY is the same as the league-average yards per carry.

Critical Concept(s)

Yardage is broken down into four categories: losses, 0-4 yards, 5-10 yards, and 11+ yards.

Based on category, yardage is assigned the following values:

Losses - 120% value

0-4 Yards - 100% value

5-10 Yards - 50% value

11+ Yards - 0% value

Hypothetical Time!

Five runs (-2 yards, 3 yards, 7 yards, 9 yards, 15 yards):

-2 yards = -2.4 yards

3 yards = 3 yards

7 yards = 5.5 yards

9 yards = 6.5 yards

15 yards = 7 yards

TOTAL = 19.6 yards

And then ...

The 8.6 yards figure is adjusted based on down, distance, situation, and opponent. Last but not least, they normalize everything such that the league-average ALY/carry equals the league-average YPC. 

Here's how we fared in 2010:

Offensive Line: 4.23 ALY (8th in the league)

Defensive Line: 3.81 ALY Against (12th in the league)

Caveat(s)

Even the Football Outsiders folks admit ALY is not perfect. They can't factor in play calling (i.e., whether a guard is pulling or blocking straight ahead). They can't factor in WR/TE/FB blocking and how it affects any given play. They can't distinguish RBs that thrive on their lateral agility from RBs that thrive between the tackles.

What say y'all? Comment early and often, and as always, GO FORTH AND BE STATISTICAL!