Eric Merrill , Mar 25, 2012; 08:53 a.m.
I don't have a 7D. I'm guessing there are custom functions similar to the 1D series, though, that influence autofocus in terms of how quickly the camera tries to reacquire focus at the same point vs passing it off to an adjoining one.
That said, you'll need to follow the subject as the subject moves, though. It's not a simple matter of acquiring an initial lock and then the camera changes focus while the subject moves all around the frame.
I would strongly urge you to look at moving the focus off the shutter button and onto a back button. There's a custom function for that. Then, your shutter only controls the shutter and exposure, while a button under your thumb controls when the camera focuses.