A metric that estimates the number of wins a player produces for his team due to his defensive ability. This number is generally calculated using full-season statistics.
Bill James first developed the concept of "win shares" as a way to determine how many victories a baseball player contributed to his team each year. Once NBA analysts began to use advanced statistics, it was logical to see if James' concepts could be carried over to NBA basketball. As it turns out, win shares can be calculated for basketball, and have become yet another metric we can use to determine what impact individual players have on their team's success.