US exchanges tend to either bust or price-adjust clearly erroneous trades retroactively.
That is good for unsophisticated customers, but it creates a disincentive for market makers to provide liquidity when there is a fat finger event. That in turn leads to larger price dislocations on such events.
(The reason is that the market maker faces adverse selection. Providing liquidity is a bet from the market maker that the price dislocation will revert.
Price adjustment reduces the profit the market maker makes from mean reversion. But if the price dislocation was caused by a real news, the market maker will eat the full losses.)
That is good for unsophisticated customers, but it creates a disincentive for market makers to provide liquidity when there is a fat finger event. That in turn leads to larger price dislocations on such events.
(The reason is that the market maker faces adverse selection. Providing liquidity is a bet from the market maker that the price dislocation will revert. Price adjustment reduces the profit the market maker makes from mean reversion. But if the price dislocation was caused by a real news, the market maker will eat the full losses.)