Block Prints And Late Trade Reports

Most exchange trades hit the public consolidated tape essentially instantly, but large privately negotiated "block" trades — often arranged upstairs between two institutions away from the public order book — are typically granted a short reporting delay, on the order of minutes, before the broker-dealer must report the trade to the tape. This exists because immediately broadcasting a huge trade would let the rest of the market front-run the dealer's unwind of any resulting inventory risk, so regulators trade off transparency for a short window that lets the dealer manage the position.

The practical consequence for anyone reading the tape is that a "block print" appearing right now describes a trade that was actually agreed upon and priced several minutes earlier, at prices and conditions that may no longer be current. A trader treating a stale block print as fresh information — for instance inferring current institutional sentiment from a trade that was actually locked in well before the market moved — is working with a systematically lagged signal, and the size and direction of block prints are more useful as a record of recent large flows than as a live read of what is happening on the tape right now.