DYAR, or Defense-adjusted Yards Above Replacement: This gives the value of the performance on plays where this running back carried/caught the ball compared to replacement level, adjusted for situation and opponent and then translated into yardage.
DVOA, or Defense-adjusted Value Over Average: This number represents value, per play, over an average running back in the same game situations. The more positive the DVOA rating, the better the player's performance. Negative DVOA represents below-average offense.
Success Rate: This number represents the player's consistency, measured by successful running plays (the definition of success being different based on down and distance) divided by total running plays. A player with higher DVOA and a low success rate mixes long runs with downs getting stuffed at the line of scrimmage. A player with lower DVOA and a high success rate generally gets the yards needed, but doesn't often get more.