Invest in the camera too....not just lenses

If you're serious about sports photography, good lenses are your best investment to capture dramatic images.  But even with the best lenses attached, the camera plays a significant role as well in getting usable images.  For example the image below was shot using a 300mm lens set at f/2.8.  The shutter speed was 1/1000s.  Yet even with this very good lens attached, the camera's ISO was automatically adjusted to 6400 to properly expose the image.  Notice there's not much grain in this image.  The grain in this image was not cleaned-up using any post-processing software.  The Nikon D700 used to capture this image performs very well at high ISO settings like 6400.  Some lesser camera bodies don't perform as well from a grain perspective when shot at high ISO settings.  These other cameras might be perfectly suitable for stills.  But to capture action in less than ideal lighting conditions, the chosen camera can have a dramatic impact on the quality of your images.