Sports photography under stadium lights is difficult even in the best environments. But if you want to capture the action in these environment, you have to get out there and shoot. Of course your equipment really matters when the lighting is poor. A camera body that has good high ISO performance helps. But to really get those photos you'll like, you probably should invest in a decent (and probably expensive) lens. A lens with a maximum aperture setting of f/2.8 is essential (and of course one that has enough reach to capture the action not close to the photographer if that's required).
The photo above was captured using a Nikon 300mm f/2.8 lens attached to a Nikon D300 camera. The camera setting were: 1/800 shutter speed, f/2.8 aperture, ISO 4000
No noise reduction was used in post-processing. This photo was just cropped and lightened a bit using Apple Aperture.
Notice how the feet are in focus sharp. But the head and ball are not. This suggests that the 1/800 shutter speed was not quite fast enough to get all of this particular action completely blur-free sharp. I used manual mode for this shot, which means that the shutter speed, aperture and ISO settings were set by me entirely - not at all automatically by the camera. I also used center-weighted metering to give more emphasis for the camera's metering processing to the subject and not to the darkness in the background as matrix metering would have done.
