Yards Per Rushing Attempt, shortened to YPC (Yards Per Carry), is the average of how many yards a player gains or loses when rushing with the ball. The number is expressed as a decimal to the tenths place (ex: 4.9).
The stat is calculated by dividing the total number of yards rushing by the total number of rushing attempts. For instance, if a player has three rushing attempts and a total of 15 yards, their YPC is five yards (15 / 3 = 5). The equation works as well for negative numbers, five carries for negative five yards is a YPC of negative one (5 / -5 = -1).
In order to be among the leaders, a player must have a certain number of rushing attempts. This is done to avoid counting players who do not have a large enough sample size for their statistics to be worthwhile.
Jamaal Charles is the leader among running backs for yards per rushing attempt with an average of 5.4 yards.
In most cases, yards per rushing attempt is a perfect place to start evaluating the performance of a running back. That being said, it does not tell the whole story. Running backs who play behind either a really talented or untalented offensive line will have skewed statistics. It isn't fair to compare those two running backs when taking this into account.
To fix this, a secondary stat should be used. A good statistic for this is yards after contact. This way a good running back is not penalized for having a bad offensive line and you can still see if they are productive with what they have.