Yards per carry is our most basic measure of a RB’s efficiency. It’s nowhere near a perfect metric, though. A long run or 2 can make a RB look better than he actually was. A guy who receives a bunch of goal-line carries will have his yards per carry skewed in the wrong direction. (A 1-yard run from the goal line is a success but doesn’t look good from a yards-per-carry perspective.)
Most importantly, yards per carry doesn’t take into account the quality of blocking a RB receives. A guy busting off 4.4 yards per carry behind an elite offensive line shouldn't be valued the same as a back with the same mark behind a bottom-barrel O-line.
We can at least solve this problem thanks to the folks at Football Outsiders and their Adjusted Line Yards. Here’s how FO describes the metric:
Based on regression analysis, the Adjusted Line Yards formula takes all running back carries and assigns responsibility to the offensive line based on the following percentages:
Losses: 120% value
0-4 Yards: 100% value
5-10 Yards: 50% value
11+ Yards: 0% value
These numbers are then adjusted based on down, distance, situation, opponent, and the difference in rushing average between shotgun compared to standard formations. Finally, we normalize the numbers so that the league average for Adjusted Line Yards per carry is the same as the league average for RB yards per carry.
Simply put, Adjusted Line Yards assigns credit or blame — in terms of yardage — to the offensive line for every running play.
We can then compare a RB’s yards per carry to his team’s Adjusted Line Yards to measure efficiency independent of blocking. Here’s what we get when we do that for the 47 RBs who carried 100+ times last season:
Kenyan Drake really pops here. He carried just 133 times on the season but averaged 18.2 per game as Miami’s workhorse over the season’s final 5 weeks. Drake averaged 4.88 yards per carry during that stretch — a tad better than his 4.76 mark over the first 11 games. If he plays as well in 2018, Drake will have no issue holding off Frank Gore and Kalen Ballage for lead ball-carrying duties.
How good was Alvin Kamara last year? He ran behind the league’s #2 offensive line in Adjusted Line Yards but still checks in 2nd here. Teammate Mark Ingram, by comparison, ranks 23rd despite a gaudy 4.89 yards per carry.
Bilal Powell: Good at football.
Jay Ajayi spent time in both Miami and Philadelphia last year, so his Adjusted Line Yards number is weighted to account for both units he ran behind. (Ditto for Adrian Peterson in New Orleans and Arizona.) Ajayi averaged 3.4 yards per carry behind a Dolphins O-line that created just 3.26 Adjusted Line Yards. Then he ripped off 5.8 yards per carry behind an Eagles squad that created 3.85.
Derrick Henry handily beats out new teammate Dion Lewis here, despite the latter averaging .75 more yards per carry last year. Lewis ran behind an offensive line that created a league-best 5.05 Adjusted Line Yards. The Titans, meanwhile, finished 23rd at 3.85.
LeSean McCoy’s 3.97 yards per carry last season was a career low. But he fares pretty well here after running behind a Bills O-line that ranked 27th in Adjusted Line Yards (3.66). The issue for McCoy is that the blocking doesn’t figure to be much (any?) better in 2018 after the Bills lost LT Cordy Glenn, G Richie Incognito and C Eric Wood this offseason.
Alex Collins’ 2017 was uber-impressive no matter how you slice it. He ranks 14th here, finished 3rd in Football Outsiders’ DVOA and led all RBs in Pro Football Focus’ run grades.
Christian McCaffrey ranked 34th among this group of 47 in yards per carry. He climbs to 24th in adjusted yards per carry — ahead of new teammate C.J. Anderson. The Panthers ranked 25th in Adjusted Line Yards (3.78).
Volume fueled Leonard Fournette to a nice 2017 fantasy season, but his efficiency was disappointing. He checks in 31st here after mustering just 3.88 yards per carry behind a Jags unit that ranked a solid 13th in Adjusted Line Yards.
Joe Mixon certainly wasn’t helped last year by a Bengals offensive line that finished 24th in Adjusted Line Yards. But he wasn’t very good in his own right. Mixon ranks 34th in this metric — 27 spots behind teammate Gio Bernard, who averaged .84 more yards per carry.
Ezekiel Elliott finds himself in poor company here. The Cowboys ranked 4th in Adjusted Line Yards (4.66) last year and helped Alfred Morris to 4.76 yards per carry. Zeke was much more efficient as a rookie, averaging 5.07 yards per carry vs. Dallas’ 4.63 Adjusted Line Yards.
Don’t go assuming Jamaal Williams will be the 2018 Packers’ starter, despite leading the team in carries and rushing yards last season. He was woefully inefficient behind the league’s 5th-ranked unit in Adjusted Line Yards. Teammate Aaron Jones didn’t hit the 100-carry threshold. But if he did, his .93 difference would have ranked 4th best.