What i don´t understand is - there are arbitrage players, who calculate "real value" of the single stocks in each ETF. Aren´t they liquid enough? Because if they were, the price would not drop that much, would it?
A lot of stocks were hitting circuit breakers IIRC, so some of the underlying single stocks simply weren't trading for part of the time.
ahh, so arbitrage players simply paused trading, as their automated calculations where incomplete?
Yeah. A human can probably spot the difference between a flash crash and a true crash, at least after making a few phone calls - but by that point the opportunity has probably gone.
I know it's anecdotal, but I have heard from some of my human prop trader friends about guys who made a killing buying on Monday morning.