Lens for Rebel XS
ROBERT CARETR wrote:
Canon 55-250mm IS
Canon EF 75-300mm f/4-5.6 III
Sigma 70-300mm f4-5.6 DG APO
Tamron 70-300mm f/4-5.6 Di LD Macro
For general use it's definitely the 55-250. Sharp, excellent IS system, light and compact. The 70-300 is a lot more money for about the same sharpness and the extra 50mm on the long end isn't much to talk about.
f/5.6 is rather slow for sport and unless it's sunny you may find that you struggle to get a high enough shutter speed. USM would help with the focus too. The Canon EF 20-200 f/4 is your best bet but may be out of your budget. The 85 1.8 is excellent value but rather limiting... I'd be tempted to either push the budget to the 70-200 or plump for the 55-250 and hope for good light. Whatever happens, you'll still get better images than a compact or bridge camera (their only advantage is that they'll have massive depth of field - the athlete will always be in focus... but so will the background..)
Good luck and let us know what you go for.