A quick-and-dirty way to measure a team’s defensive skills.
Defensive efficiency (DER) is a very simple statistic for measuring how well a team’s defense performs. It is simply the percentage of balls put in play that are turned into outs. Bill James developed this statistic in one of his abstracts during the 1980s. This statistic applies only to whole teams.
This formula might look a little out of place here; I describe most fielding statistics later in the chapter. However, DER is strongly related to the defense independent pitching statistics (DIPS) formula (see “Measure Pitching with DIPS” [Hack #51] for more information). This formula is essentially the same as batting average on balls in play (with a couple of subtle differences). Before we start talking about DIPS, we need to talk (just a little bit) about defense.
Standard statistics don’t tell us much about how a team performed defensively. We’re stuck with only a few coarse measurements:
Strikeouts of opponents
Home runs allowed
We want to show how well a team created outs from balls put in play. Unfortunately, errors create some problems for us. First, the difference between a hit and an error can be subjective. Additionally, errors can occur at times other than when balls are put in play (for example, passed balls by the catcher, missed fouls, or bad throws on putouts). So, the formula here is just an approximation if we use ...