I uploaded two football images shot with the EF70-200mm f/2.8 L IS USM. This will give you a pretty good idea of what you can expect to in the daylight and the dark.
Canon 5D MKII, Canon EF70-200mm f/2.8 L IS USM, Av, 200mm, f/3.5, ISO-800, 1/640
Canon 5D MKII, Canon EF70-200mm f/2.8 L IS USM, Tv, 200mm, f/5.6, ISO-6400, 1/800