You want faster glass, and that doesn't come cheap. You want a lens with a maximum aperture of at least f/2.8. For sports, you probably want the Canon 70-200mm f/2.8 ($1,300), the Sigma 70-200mm f/2.8 ($800), or the Canon 200mm f/2.8 ($750). You can get even faster (Canon 200mm f/2) or longer (Canon 300mm f/2.8), but the prices for those are well over $4,000.