Fitzgerald on Scooter Libby

I think the meat of Fitzgerald's press conference today came in a couple sentences of baseball metaphor. He compared his investigation with an umpire trying to look into a batter who just got hit with a pitch.

"What we have when someone charges obstruction of justice, the umpire gets sand thrown in his eyes. He's trying to figure what happened and somebody blocked their view."

Fitzgerald is accusing I. Lewis Libby of throwing sand in the eyes of the investigators. Why would Libby do that? Is there something to hide? If there wasn't - and it certainly is possible it was a small issue - why cover it up?

(Also: At what age should one stop using the nickname "Scooter"?)