Alfred Morris’s 1,613 rushing yards is the third highest total for a rookie in NFL history. It ranked second this year, behind only Adrian Peterson’s amazing record-threatening total. He played in an unconventional option-style offense behind a young quarterback with rare skills. It was an unexpected season from Morris, and an uncommon season for any running back. By all conventional measures, Morris’s season was a runaway success.

Although his rushing yardage total and his 13 touchdowns can’t be denied, more advanced measures of performance suggest Morris’s impact was more modest. Morris totaled only 4.8 Expected Points Added (EPA) for the year, which ranks 13th for all league running backs. EPA measures total production for a player in terms of net point differential. It includes all run and pass plays, and even turnovers. That 4.8 EPA is barely above a neutral impact. To put it in perspective, Robert Griffin III totaled over 138 EPA for the season.

Morris’ four fumbles, which rank tied for third in the league, explain part of the difference between his conventional totals and his EPA production. The other major explanation is his Success Rate (SR), a measure of the proportion of plays that result in an increased chance of scoring for an offense. Morris’ SR was 43%, which ranked 13th in the league. That’s above average, but not league-leading in the same way his yardage and touchdown totals are. It means that well over 50% of his touches were setbacks for the Redskins–short gains, stuffs, or even tackles for a loss.

Much of that 57% ‘non-success’ rate shouldn’t be attributed to Morris. Much of the responsibility falls on the offensive line. And in general, running is over-used in the NFL, particularly on 1st and 2nd down, which makes it easy for defenses to key on runs.

The success that Morris did enjoy in 2012 can also be attributed to offensive coordinator Kyle Shanahan’s option scheme, and Griffin, who made it possible. The scheme effectively removes a tackler from the equation on nearly every run, which frees an offensive lineman to help open a hole, making life a little easier for a running back.

We can see the effect that Griffin and the option had on Morris’s production by looking at the week 15 game against Cleveland, when Griffin was sidelined by a knee injury. It was Morris’s toughest outing of the season, with only 87 yards on 27 carries for a 3.2 yard per carry average. Most fans would point to his two touchdowns as evidence of excellent output. (After all, that’s worth 12 fantasy points!) But that’s a terrible way to measure running backs. They should be expected to score in goal-to-go situations. His total impact in the game, despite the two scores, was slightly negative in terms of EPA, and his SR was close to his worst of the season at only 28%.

None of this analysis is intended to say Morris is sub-par or flawed. The point is that Morris’ impact on the bottom line this season was not as big as his conventional  numbers suggest, and much of his success can be credited to his quarterback and the offensive scheme.