This baseball statistic is used to measure the defensive effectiveness of a team in converting batted balls into outs by the fielders. Defensive efficiency rating (DER) is calculated by comparing the number of hits allowed, not including home runs, to the defensive opportunities, which are all balls hit into play except home runs.
The formula for DER is: 1-((H-HR)/(PA-HR-BB-HBP-SO)).
Also referred to as "Def Eff" or "Defensive Efficiency Ratio".
The purpose of DER is to determine the overall effectiveness of the fielding defense of a baseball team. The higher the DER, the better the team's fielding ability is considered to be.
While pitchers who are credited with a lot of strikeouts tend to prevent runs from scoring, those who pitch to contact would benefit more from a high team DER. This rating can also be calculated for individual players, which is a useful statistic to determine the likelihood of a team's ability to prevent runs within a particular lineup (considering both the participating pitchers and fielding players).