Basically if a stock on Nasdaq drops 10% a circuit breaker is...

Basically if a stock on Nasdaq drops 10% a circuit breaker is put in place that prevents shorters from continually lowering the the offers pushing down the price. Its supposed to mitigate a freefall from shorters plowing into a stock that is seeing high selling pressure. Since shares don't have to be delivered for three days, this tries to keep the price in some sort of stabilization.