Well, running will improve stamina some. I'm with the others about outdoor running being much better and easier than treadmill running. About the sport thing, I'm not so sure. I mean, it really depends on what kind of shape your in now. If you're already somewhat fit, then improving your long distance running may help you in sports less than you think. I am only reasonably fit, but I can run for rather long distances (not quite marathons, but close), but I'm still not much faster than my friends when messing around in sports, even though I can run about 10 times farther than the person I'm thinking of. I think that's because sprinting/burst endurance is very different than long distance endurance. We had a good thread on that kind of excercise a bit ago. Try looking that up.