Two Suggestions:


1) if your only interested in the action at 3rd base then focus and 3rd base and turn off autofocus


2) If your using a 40D or higher then you should have no trouble with accurate tracking. I've used my 40D in exactly the same situation center focus point with a 70-200 f2.8 iso 3200 at f2.8 and 1/400. Use noise Ninja and go higher than 500 Iso. By the way. Nothing, I Mean Nothing (perhaps the Mark IV) focuses faster or more accurately than my old 1D at $384.00 it is by far my cheapest camera and runs rings around my 40D and 1DIIn. Never change to multiple focus points unless you want the crystal clear expression of the short stop watching the slide into 3rd.