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How Order Books Uncross After a Trading Halt

Article Quant Q&A · Author: Eugen
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Summary

The document explains why a stock's displayed bid can exceed its ask during a trading halt. On the cited US venues, including Nasdaq, BX, and PSX, orders can arrive and become ready to trade while the halt prevents executions. The resulting visible book may therefore appear crossed, with bids priced above offers, without indicating that the displayed data is necessarily a software error.

When the halt is released, the accumulated orders are matched or deleted, and the market uncrosses. This explanation is specific to the described venue behavior and does not detail how every exchange or halt mechanism handles queued orders. The observation concerns order-book state during a halt, when displayed prices cannot be interpreted as an immediately executable market.

Key ideas

  • A halted market can accumulate orders that would otherwise be ready to trade.
  • The halt prevents those orders from executing even if the displayed bid exceeds the ask.
  • When trading resumes, queued orders may match or be removed as the market uncrosses.
  • Order-book behavior during a halt depends on the market and its rules.

Tags

EquitiesMarket microstructureExecution
Full text
# Order Book during trade halts


# Order Book during trade halts












I noticed this weird structure of the order book during trade halt of $GCT, August 19th 2022. Stock was halted at the time. Could someone explain why bid is higher than ask?

Is this just a bug in the webull app or can the order book really look like this?

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## Answer by JoshK (score 3, accepted)

https://quant.stackexchange.com/a/71974

Depending on the market. You will see on ITCH US markets (NASDAQ / BX / PSX ) the orders come in ready to trade. But the market can't trade them because of the halt. As soon as the halt is released then everything pairs off or deltes and the market then uncrosses.

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.