Never go below 500 shutter speed for sports. At 500, you may occasionally see slight motion in your images but they won't be blurry. Some shooters actually like the look of an arm or hand having slight movement in their images.
If you want to absolutely freeze the action from any sport, try to get to 1600 shutter speed or higher.
The higher the shutter speed, the more details you'll see. Check out this post on how higher shutter speeds can add more detail to some images.
The image below was created using 1600 shutter speed, which is why you can see the individual sand grains flying up at the bottom of the runner's shoe.
(Photo by Travis Bell)
