A steep stock-market selloff on Thursday again had investors on the lookout for a potential trading halt, as the S&P 500 slipped toward the threshold that would trigger an initial “circuit ...

The steep selloff was again threatening to put the market's circuit-breaker rule in play. That dictates that a fall of 7% for the S&P 500 before 3:25 p.m. Eastern time results in a marketwide ...