There's Citadel Asset Management, the quant hedge fund (which is probably the one that lent money to Melvin, though I'm not sure about that), and Citadel Securities the HFT / market-making show (they have the same owner).
HFT market-making using retail order flow isn't front-running - the price the customers get is the same regardless ("Best Bid Offer" as brokers are legally required to provide in the US). The difference is, once that the HFT market maker holds the stock, they can get rid of it more easily (i.e. they can close the trade) because (the assumption is that) the retail flow is "noise" (uncorrelated with future price movements) as opposed to professional/institutional traders (e.g. other hedge funds executing their strategies), where a big problem is negative selection (i.e. you're more likely to execute a trade with someone that has better information than you).
For instance the bid side may say
Alice wants to buy 50 shares at $20 (order added at 10:37)
Bob wants to buy 30 shares at $20.1 (order added at 11:18)
Citadel wants to buy 35 shares at $20.1 (order added at 11:17)
David buy 10 shares at $20.1 (order added at 11:01)
The bids are ordered by price, and ties are broken by who placed the order first.
If Evelyn (Robinhood customer) shows up and wants to sell 5 shares at $20, then the exchange will say, oh nice 20 is less than $20.1, lets get some trades going! $20.1 is the highest prices, and of those orders David's were entered first. So Evelyn's sell order is matched with Davids buy order. The price is determined by the order which was in the book. So Evelyn will get a better price than she hoped for!
If Evelyn had requested to sell 100 shares, then she will first sell to David for $20.1, then Citadel's for $20.1, then Bob's for $20.1 and finally some of Alice's shares for $20.
Ok but what happens if Citadel is paying for order flow?? Now the order book (from Evelyn's perspective) looks like
Alice wants to buy 50 shares at $20 (order added at 10:37)
Bob wants to buy 30 shares at $20.1 (order added at 11:18)
David buy 10 shares at $20.1 (order added at 11:01)
Citadel wants to buy 35 shares at $20.1 (order added at 11:17)
So if Evelyn (Robinhood customer) shows up, and again wants to sell 5 shares at $20, then she will sell to Citadel, even though their order is later than David's.
So to sum it up
Evelyn (Robinhood customer) is unaffected
Citadel wins
David loses.
[1] https://www.sec.gov/fast-answers/answersbestexhtm.html
Robinhood publishes their execution numbers (as required by the SEC), along with other brokers. At a quick glance, there is nothing out of the ordinary. It's also worth noting that you cannot directly compare numbers as different platforms have different trading behavior.
https://robinhood.com/us/en/about-us/our-execution-quality/
In fact, they were still seeking "best" execution; they just didn't beat other brokerages because of high payments for order flow and misled customers about that.)
- Rebates from market makers and trading venues
- Robinhood Gold
- Stock loan
- Income generated from cash
- Cash Management
https://robinhood.com/us/en/support/articles/stock-order-rou...
Legally not, illegally... yes, and try to prove that.