IS is nice, if you can afford it...
Agreed...but, when shooting sports, you're going to want to keep the shutter at least in the 1/500 and above range to stop subject motion, and you need some pretty bad Parkinson's for IS to make a visible difference at those shutter speeds.
That's also why you want the fastest lens you can get for sports, so you can get the fastest shutter speeds. An extra stop of lens speed means one stop lower ISO setting, basically. That's not very important outdoors on bright days, but it quickly becomes a factor when the clouds come out and it's your overwhelming concern when the Sun goes down.
...but, of course, ISO speed is closely tied to what you're doing with the image. If you're just posting small pictures to FaceSpace, you can get away with much high ISO settings than if you're a stringer for Sports Illustrated
There's one other caveat that I've gotta bring up. Those SI
guys generally shoot with two lenses on two bodies, and for a very important reason. The secondary setup is with a 70-200 f/2.8. The primary setup is with a 400 f/2.8. They're right there on the sidelines, as close to the action as you can get without being part of it, and they still need 400mm lenses to get the shots they do. The 70-200 is what they (quickly) switch to when the action moves to right in front of them, but most of the time they're using the 400.
So, again, if you're not looking for something to make posters with and if you're not in the nosebleed section, you can shoot from the stands with a 70-200...but you should plan on heavily cropping every image, and you should expect to have the lens always at 200. And you'll especially want the fastest lens you can get, because cropping exaggerates high ISO noise at the same time it makes the image softer.
If, indeed, you are
shooting from the stands...well, first, I'd suggest that you adjust your expectations accordingly. And then I'd suggest resigning yourself to the fact that you're not going to get great images no matter how much you spend. And then I'd suggest preparing yourself to be disappointed even after spending lots of money. Starting to get the picture?