Several people reciently have posted comments that defensive metrics weren't very good. FCB humerously posted that it would be best to forget them all together and save yourself the trouble.
What are the short commings of these metrics? Is there something inherrent to defesense that makes it hard to measure in statistical terms?
This is a serrious question, not a swipe at stats. I'm currious about the methodoligies that go into defensive metrics and why they aren't as usefull as offensive ones.