I absolutely LOVE the Canon 2.8 especially since it has the image stabilization, although I would like the 300, it's a bit beyond my reach. I would speculate that this lens is similar in kind as it is an L series, I think. Is this constant 4.0 aperture throughout the lens?
You might be able to shoot night work, but you may have to bump the ISO up a good deal. Football fields are often pretty well lighted but since all the lights are so high they can create oddball shadows at times. I have had trouble with this with night time softball but still pulled out some images. I also have the 100-300 f4-f5.6 and wish I had saved the cash and went for a L series high end prime. Nice for daytime sprts but not so good at night.
Saw the night time baseball sample and looks as though it will be usable ...