it's all in the timing, watch the ball and start holding down the button half way to focus the camera before the pitcher pitches, and press the button slightly before he hits the ball.... your most likely going to get a bunch of strikes while trying to do it, but thats the only way with a normal camera
also i would suggest using a tri-pod for sharper pictures, and zoom in more for better framing... if you use a tripod, you can set your frame accordingly, and then you can put all of your effort into the timing.
