Former Citadel Securities director explains what happened with Robinhood and GameStop last week

Stock markets have seen unprecedented levels of trading in recent days, fueled by retail trading activity tied to Wall Street Bets. Robinhood — which became the key figure in this drama as the venue through which much of the publicly visible trading occurred — has been a focal point of this market backdrop after buckling under the pressure of heightened activity and temporarily limiting purchases of certain stocks, like GameStop and AMC. 

In response, Robinhood came forward and tied its response to the underlying settlement infrastructure. Robinhood said in a blog post that the limits on trading were connected to soaring clearinghouse deposit requirements. The firm later said that a move to real-time trade settlement would remedy f the issues that faced not only Robinhood but other brokers. Here's from the blog:

"The clearinghouse deposit requirements are designed to mitigate risk, but last week’s wild market activity showed that these requirements, coupled with an unnecessarily long settlement cycle, can have unintended consequences that introduce new risks."

Shane Swanson of Greenwich Associates — a market structure wonk and former director at Citadel Securities — breaks down exactly what happened to the markets last week and why things stopped trading on a new episode of The Scoop podcast.

Here's Swanson:

"I like to use examples because I am a simple guy and examples seem to help. If I am a broker and I have $10,000 worth of capital and these aren't the accurate numbers, but say that allows me to trade $100,000 worth in the market because I have some leverage capabilities. And I am going to let somebody trade with me and I am to give them margin which means I'm going to lend them money and they're going to trade, and I am exposed to that lending risk. And they trade all the way up and they use all my $100,000 that I am allowed to expose myself to, once I hit that $100,000 I can't trade anymore. I can't expose myself to any more risk. I have used up the bucket of capital of which I am allowed to trade now."

As for what happens next, Swanson told The Scoop that "it's always hard to go backwards on cost," referring to the ramifications of moving from T+2 to a more instant settlement process.

"It all depends. If the costs are egregious enough that the industry has to absorb commissions could come back. Movement from T-plus 2 to T-plus 1 settlement would be over a long enough time horizon I believe that would not be something that ends up impacting the retail investors in terms of cost," Swanson explained.