I personally have a 70-200mm f4 non-IS lens and the 70-200mm f2.8 IS lens and shoot a lot of sports and dance and I can state categorically that the 2.8 IS is the way to go. Reason is you will definitely need the speed of the 2.8 for low light conditions, yes 1 f-stop can be critical and you need to the IS not for the competitors but for you. If your shooting just football it wouldn't make a difference but dance, basketball, volleyball, cheer frequently require a lot of movement and this does not lend itself well to using a monopod. That said I got a lot of good shots with my 70-200mm f4 lens and even a few published so the capability is there. If you go with the non-IS f2.8 don't ever upgrade to the IS version or you'll kick yourself in the behind for years.