Moving the Whale

In Chapter 15, Larry Harris takes us away from the public exchange and into the “Upstairs Market.” If you want to buy 500,000 shares of a stock, you don’t just dump a market order into your app—you’d move the price 10% against yourself before the order was half-finished.

You need a Block Trader.

The Four Block Trading Nightmares

Large traders (Block Initiators) face four massive problems:

1. Latent Demand: The people who want to sell to you aren’t standing in the market with orders. They are “responsive traders” who will only trade if someone calls them with a good deal.
2. Order Exposure: If the world knows a huge buy order is coming, everyone else will buy first (front-running), pushing the price up before you can even start.
3. Price Discrimination: If you buy 100,000 shares from a dealer, they are terrified you have another 400,000 shares behind it. They don’t want to be the “first loser.”
4. Asymmetric Information: Dealers assume if you’re trading that big, you must know something they don’t. They demand a “price concession” (a worse price) to cover their risk.

The “Upstairs” Solution

Because of these problems, block trades happen via phone and private networks.

• Block Brokers (The Assemblers): They use their Rolodex to find 10 different institutions to take pieces of your order.
• Block Dealers (The Positioners): They take the whole trade onto their own books and then slowly sell it off over days or weeks.

The “Wolf Audit”

To get a good price, a block initiator has to prove they aren’t a “wolf” (smart money). They have to convince the block trader they are just a “sheep” (uninformed/utilitarian).

• A “Good” Story: “Our pension fund is rebalancing,” or “We need to raise cash for a big acquisition.”
• A “Bad” Story: “We think this stock is going to moon in three hours.” (No one will trade with you if you say this).

80% of Blocks are Sellers

Here is a weird stat: In the US, 80% of block trades are initiated by Sellers. Why? Because it’s much easier to prove you’re an “uninformed” seller. You might need cash for taxes or because of a legal requirement (like ERISA rules for pension funds). Buyers, however, can buy anything—so if they are buying this stock in this size, everyone assumes they have inside info.

The Size Precedence Rule

When a block trade is finally matched upstairs, it has to be “printed” on the exchange. In the US, if the trade is over 25,000 shares, it gets Size Precedence.

• The Rule: It can jump ahead of other orders at the same price, but it must “clean up the book” first by filling any orders at a better price. It’s a compromise between the pro block traders and the public limit order traders.

Summary: Trust is Everything

Block trading is the only part of the market that cannot be automated easily. It relies on reputations and relationships. If you lie to a block trader about your order size, you’ll be put in the “doghouse” and nobody will take your calls for a long time.

Next time, we look at the ultimate providers of liquidity: the Value Traders.

Next Post: Value Traders: The Final Boss