When does the NYSE halt trading?

SallyG answered one month ago …

Good question! I wish I knew the answer, as I thought it would have been a good idea, to prevent investors from acting instantly on their panicked reactions. I think there is a percentage change that suspends trading, but I don't know what it is.
Suspending all trading would have made more sense to me than just suspending short selling of financials—less subjective, anyway. I suspect the reason that they didn't do so is that "they" thought it would send a negative signal, but IMHO there could be no signal more negative than the unrestrained free-for-all of the last week or so.