I think this actually has much less to do with "protecting" the stock market (as discussed in comments), than protecting the ruble. Because for sure the majorit

I think this actually has much less to do with "protecting" the stock market (as discussed in comments), than protecting the ruble. Because for sure the majority of foreign investors will want to sell their securities ASAP and exit the market in USD, not rubles. And therefore that'll create a large pressure on the ruble.