The Depository Trust & Clearing Corporation settles most listed securities transactions in America; in 2011, it did $1.7 quadrillion [1]. You've never heard of it unless you're a professional trader, but it's actually quite fascinating to read up on.
Trading looks instantaneous. But settlement takes a few days. In between are a series of credit agreements. From your broker to you. From the clearinghouse to the brokers. DTCC is the clearinghouse. Robinhood is the broker.
There are rules and contracts between DTCC and its members, including Robinhood [2]. Those contracts ensure that when you buy shares through your broker from a Robinhood customer, if Robinhood falls down two days later, there is collateral sufficient to make you whole. Those collateral requirements change in reference to, amongst other things, the volatility of the security. (If a broker falls down, the clearinghouse liquidates their collateral and makes their counterparty whole. More volatility means more chance the collateral will be insufficient.)
In this case, collateral requirements on GME went up. Because of its volatility. So while before Robinhood had to pony up collateral for a few shares of GME for every hundred it traded, it now had to, at close of business, pony up one hundred shares' worth of collateral for every hundred it traded. That creates a cash crunch. One that exacerbates itself with every additional trade in the security. If Robinhood fails to satisfy those collateral calls, they go out of business overnight. Into receivership. Done.
Most brokers have policies for these situations. Higher brokerage fees for securities on a schedule. Not making shares and cash from trades available until the trade settles, sort of like what banks do for large cheques. But I don't know if Robinhood is able to do that quickly. So instead they pulled the plug.
[1] https://en.wikipedia.org/wiki/Depository_Trust_%26_Clearing_...
[2] https://www.dtcclearning.com/products-and-services/settlemen...
Trading looks instantaneous. But settlement takes a few days. In between are a series of credit agreements. From your broker to you. From the clearinghouse to the brokers. DTCC is the clearinghouse. Robinhood is the broker.
There are rules and contracts between DTCC and its members, including Robinhood [2]. Those contracts ensure that when you buy shares through your broker from a Robinhood customer, if Robinhood falls down two days later, there is collateral sufficient to make you whole. Those collateral requirements change in reference to, amongst other things, the volatility of the security. (If a broker falls down, the clearinghouse liquidates their collateral and makes their counterparty whole. More volatility means more chance the collateral will be insufficient.)
In this case, collateral requirements on GME went up. Because of its volatility. So while before Robinhood had to pony up collateral for a few shares of GME for every hundred it traded, it now had to, at close of business, pony up one hundred shares' worth of collateral for every hundred it traded. That creates a cash crunch. One that exacerbates itself with every additional trade in the security. If Robinhood fails to satisfy those collateral calls, they go out of business overnight. Into receivership. Done.
Most brokers have policies for these situations. Higher brokerage fees for securities on a schedule. Not making shares and cash from trades available until the trade settles, sort of like what banks do for large cheques. But I don't know if Robinhood is able to do that quickly. So instead they pulled the plug.
[1] https://en.wikipedia.org/wiki/Depository_Trust_%26_Clearing_...
[2] https://www.dtcclearning.com/products-and-services/settlemen...