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DER and You

DER is the ratio of balls in play that are turned into an out. Think of it as the inverse of BABIP. Coming into play today, the Mariners defensive efficiency ratio stood at an awe-inspring .678 meaning that Mariner defenders turn 67.8% of balls in play (e.g. HRs excluded) into outs. That is dead last in the American League and only the lowly Pirates have more shame than us in the National League.

Now, there's a pitching aspect to DER as well. Line drives only end up as outs roughly 30% of the time compared to groundballs, bunts and flyballs which all hover around 80% outs. Infield flys are a touch over 90%. Of course, this all varies depending on whose definitions of line drive vs flyball, flyball vs popup, etc that you use, but they're good general guides. So a pitching staff that yields more line drives than usual is going to see a lower DER that's not the fault of the defenders. This was part of the hope for the 2008 Mariners that removing the suck fests of Weaver and Ramirez would make our defense look slightly better.

Well, it hasn't. The 2008 staff is allowing a dead-on league average 19% line drives. They are allowing slightly more flyballs than usual and, since they have an average IF/FB ratio, they are getting more infield flies than average. So, if anything, the pitching staff is gifting the defense easier balls in play than the average American League team. You can see this quantitatively on the THT Team page in the Plus/Minus under Team Fielding Stats. You see both a pitching and a fielding number. That pitching number is exactly what we just described, the number of plays the defense should make over an average squad due to the pitcher's batted ball profile. So, we possess the league's worst defense at turning balls in plays into outs even with some extra help from our pitchers.

The average team faces about 27 balls in play per game. The difference between the Mariners defense and an average AL defense so far is a little over half an out per game, meaning the Ms defense allows a bit over one runner to reach base every two games that an average defense does not. The difference between the Mariners league-worst defense and the Blue Jays league-best defense is over 1.25 batters every single game. Every. Single. Game. In relative terms, Mariner pitchers have to record 28.27 outs every game compared to Toronto's 27.

Defense is not a strength of ours.