This is the number of yards a team must gain for every 7 points they put on the scoreboard. (That's the inverse of "points per yard allowed," which is in the title.) The formula: 7 / (total defense/scoring defense).
In other words, teams that score 14 points against Alabama will have an average of 343 yards. It takes only 280 yards to amass 14 points against BYU. By the way, #123 in this list is Southern Miss, with 71.5 yards. That 343 yards you manage against Alabama would get you 33-34 points against USM.
