I just bought a 1D Mark II for photographing my kids' football games. I'm wondering how most 1D users set the auto-focus points for football. I assumed one of the top center points would be best, but I see there are custom functions to limit the number of selectable AF points to either 7 or 9.

I usually shoot the 70-200 f2.8, sometimes with the 1.4 II extender, usually set at f4.0, from the endzone.

What's best for keeping the ball carrier in focus with a 1D?