Question regarding the market disruption

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6. partly it's the unexpected aspect of it; but it's mostly the pros who panic

well, others panic because they're told to and/or because they see the pros panic.

but most people don't trade overly frequently and not being able to trade for a particular couple of hours during which they likely wouldn't have traded anyway isn't really a cause for panic.

the pros, however, might get caught in the middle of a huge complex trade, expecting to take 3 milliseconds of risk to clip a tiny profit and wind up taking 3 hours of risk. it turns a complex, carefully planned business model into one big gamble and you didn't really even get to choose the bet.

to make it a bit more clear, many pros do not hold positions when the markets are closed, period. certainly they don't hold risky positions over the weekend. but they do take risky positions during the day in the expectation that they will get out of those positions before the end of the same day, often only minutes or seconds later; or, in the case of automated high-speed trading, milliseconds.

the trading halt means they are unexpectedly taking a huge and risky position for hours when the market is effectively closed, something not in their business plan.

that said, trading halts do happen, so that's part of the risk of that line of business. moreover, in this case, trading is still possible, just not at the nyse in particular. there are other places to trade nyse securities.