buying & selling the same amount of shares ( what some are refering to as frisbee trading ) would have a net zero effect on SP. as we all know stocks rise when there are more buyers than sellers and vice versa. when stocks go up or down on significantly larger than average volume, that can indicate a major change in price direction. frisbing stocks back and forth will only increase volume but should'nt effect SP because equal amount of buying and selling. I'd be interested in learning how stock frisbee trading can influence the market in either direction...if anyone has an explanation...