Higher ISO= Higher Noise
Less Light=Higher ISO
Stadium Lights and Lights in Gym's may look bright but if you took out a handheld light meter and read the area or a "spot" you would see that the levels are actually quite low. Your eye may fool you into thinking the light level "looks" a lot higher than you would ever think!
A flash will do little to help light up a kid 30 yards away on a football field-most flash's really drop off on lighting up a scene after about 30 ft-Studio Strobes will reach farther.
Solution is FAST PRIME LENSE of 2.0 or more which when you are looking at 100mm or bigger=$$$$$$$.
http://www.bhphotovideo.com/bnh/cont...sc&fi=all&pn=1