Invented by Jim Furtado, extrapolated runs is a statistic used to measure a player's performance, and it is calculated by multiplying a player's total in each of many positive offensive events (stolen bases, singles, walks, etc.), as well as negative events (grounded into double play, caught stealing, etc.), by a specified weight attached to each event, and subtracting or adding the products. It is a way to accurately measure how many runs a player truly contributes to his or her club.
Sabermetrician Jim Furtado created this statistic to give teams a more accurate measurement of each player's true value to his/her team. Extrapolated runs is very similar to runs created (RC), which was invented by Bill James, but uses a formula of linear weights that gives a different value to each positive and negative event, rather than the simple multiplicative formula used by James. This allows good hitters on poor teams to be recognized in a positive light for how good they are, without focusing on a possible low RBI or run total-i.e. things that aren't entirely under a player's control.