Wow, this is a subtle one. Okay, let's analyze. First, the phrase "law and order" is so common in our culture that it spawned a TV franchise. "Knife and _____" has no such cliche, so no help there. Let's focus on details, then. Law is a set of rules designed to keep the order, so order results from law. What results from a knife? Nothing specific.
The only thing I can imagine as an answer is "sheath", but even then the order is backward; a sheath is that which contains the knife, so it should be in front of it to form a proper analogy.
In short, I see no obvious right answer, and this is as close as I can get.