Question: Is Defense Efficiency related to pitching or is it an independent way to measure a teams defensive ability?
Note: Defensive Efficiency, is the rate at which balls put into play are converted into outs by a team's defense. Def Eff can be approximated with (1  BABIP), if all you have is BABIP, but a team's actual Def Eff is computed with (def from Baseball Prospectus http://www.baseballprospectus.com/glossary/index.php?search=def%20eff):
1  ((H + ROE  HR) / (PA  BB  SO  HBP  HR))
Why I asked the question: On the surface, I thought Defense Efficiency would be a good way to determine how well a team is doing defensively, but I noticed is that teams with worse pitching had lower Def. Eff. Ratings. I looked to see if the two were actually correlated.
Analysis: Comparing a team's Def Eff vs. the team's ERA. I chose ERA because it is a commonly used and understood. Also it is a decent measure of team's pitching ability. Data from 2004 to 2007 was used. Here is a chart of the results:
There is definitely a direct relationship when these two are plotted against each other. Then I had Excel create a linear trend line (for ease in future calculations) and the formula is:
Expected Def Eff = 0.0163 * ERA + .7702
Finally I subtract the actual value from the expected value and get how the team is doing defensively. I know this method is not perfect, but it is better than Def Eff by itself since it takes the teams pitching into account.
Seeing Defense

Joe Posnanski teams with Tom Tango to compare the fans scouting report on
defense (the eyeball test) to the numbers computed by advanced defensive
analysis...
1 hour ago
No comments:
Post a Comment