The problem is it's not a judicial matter. To my knowledge, there's no legal exposure for Meyer. It's about perception and position. What you've described about letting things run their course, or giving the benefit of the doubt is fine if you're an average schlep. It isn't fine when you're the face of a football team, university, and to some extent an entire state. You're paid at a different standard, and are thus held to a higher standard. It will be very difficult to prove without a doubt that Meyer knew and elected to do nothing. But it will be impossible to prove he knew nothing and is completely innocent in what is a very sensitive matter.
What you've alluded to about this all being smoke, and the works of a manipulative crazy woman are fine if the charges were against him. He could have his chance to refute the claims and survive. But this is about essentially looking the other way, potentially again and again, without forcing the authorities to determine if she's just a big liar or if one of his coaches is beating his wife on a regular basis. His decision--or even Shelley's decision--to do nothing is the killer.