Explanation:

Each individual rush is considered on it's own, and measured by it's "success." A run is considered successful if it gets 40% of the yardage needed to move the chains on first down, 60% of the yardage needed on second down, and 100% of the yardage needed on third or fourth down. This is a much more accurate overall picture of how well a running back does in a game than just the total yardage or ypc averages because it ignores big run outliers that can skew those kinds of stats

Stats after the jump.