Fielding percentage is the statistic that has traditionally been used to measure defensive ability, but it fails to account of a fielder's range.[B] Fielders with ample range on defense are able to make plays that most players would not have the chance to make. Defensive Runs Saved was created to take into account range when measuring a player's defensive ability. To calculate Defensive Runs Saved, for each ball hit, points are either added or subtracted to the fielder's rating depending on whether or not they make the play. For example, if a ball hit to the center fielder is expected to be caught 30 percent of the time, and it is caught, the fielder gains 0.7 points. If the center fielder does not catch the ball, he loses 0.3 points.
The formula
DRS uses Baseball Info Solutions data to chart where each ball is hit. Say, for instance, a center fielder sprints to make a nice catch on a fly ball. Then, say data from BIS tells us that similar fly balls get caught 60 percent of the time. That center fielder gains, essentially, 0.4 bonus points for difficulty. If he can't make the play, he loses 0.6 points. At the end of the day, that player's overall score gets adjusted to the league average -- and then that score gets adjusted for how many runs the once-adjusted score is worth.
Why it's useful
Because errors and assists barely scratch the surface of what makes a successful defender, DRS exists to help better value defenders for their range, positioning and first step.