I hate to question McCarver (yeah right) but I've never heard of this ruling, and after 30 minutes of searching the official rulebook, I can't find a definitive answer. I think he's an idiot, but I've been wrong before.
Situation: Runners on 1st and 3rd, 1 out.
Batter hits a pop fly into foul territory, 1st baseman tries to make a play, but bobbles the ball, slapping it up into the air a couple times, almost making the catch, but eventually drops it. Runner on 3rd tags up and takes off towards home right when the 1st baseman first touches the ball (before the subsequent bobbles).
McCarver says "The runner at 3rd can go immediately when the fielder touches the ball. He doesn't have to wait until the fielder catches the ball."
Is that right? I always thought it had to be an official catch. In other words, the out had to be made before you could advance. It's a moot point on this play obviously, because the fielder dropped the ball, but I'm interested in knowing if this was yet another idiotic statement by McCarver, or if he actually taught me something tonight.
ETA: If he IS correct, please point me to the official rulebook if you can find it, because I'd really like to see where I'm missing it.