Offenses and defenses are generally ranked based on points scored and points allowed. The problem is, that doesn't account for different conditions faced by each squad.You'll face similar problems when creating metrics for Lean operation.
As a leader in a Lean organization, there is a lot of pressure on you to hit your metrics. It can take a lot of moral fortitude to choose the harder right over the easier wrong.
What are "problems", and why are they so hard to solve? Learning the barriers to problems is the first step in tearing them down so you can solve them better.