What happens when the underlying S&P 500 Index hits a circuit breaker level?

A 7% decline (Level 1 circuit breaker) in the S&P 500 Index before 2:25 p.m. CT will trigger a NYSE Rule 80B trading halt for both the cash equity market AND all U.S.-based equity index futures and options, including E-mini S&P 500 and S&P 500 futures and options. Trading will resume once trading in the cash equity market resumes, with price limits expanded to Level 2 (13%).

http://www.cmegroup.com/trading/equity-index/faq-sp-500-price-limits.html

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