“The NFL should create a policy about when they will penalize a players’ criminal conduct and when they don’t, and then follow it, “
The big problem is that criminal conduct is hidden. Hidden by the players, coaches, administration and civil authorities.
I don't understand your point. Criminal conduct that is not discovered is by definition unpenalizable. I think we are all talking about conduct or alleged conduct that other people actually know about. Criminal conduct that is "hidden" by coaches, administrators or civil authorities is itself criminal conduct. Criminal conduct by law is public, initiated when someone is arrested or a complaint is made. Pretty hard to hide that.