Circuit breakers that stop trading in individual stocks or the entire market if prices drop too fast have been widely introduced after the 1987 stock market crash. Circuit breakers get triggered frequently during financial crises, of which we obviously had quite a few in the last three decades. In general, they are a blessing because they allow traders to calm down and assess the situation without having to make snap judgements in a panicky situation.
I am analyzing (as part of a larger study that I am carrying out) what seems to be a significant correlation both for p value and for effect size between volumes and returns on the front contract of the eminisp500. With an increase in volumes compared to a baseline purified by rollovers and precisely by circuit breakers and holidays, there are tendentially negative returns on the eminisp500.