Interpreting an Extreme After-Hours Stock Print
Summary
The document considers a sharp, isolated downward move in an after-hours stock chart that quickly returns to its previous level. One answer identifies a specific small print as an average-price trade reported through the Alternative Display Facility, and says its fractional price could not have been posted directly to an exchange. This suggests the displayed print may be linked to another transaction rather than representing ordinary trading at that level.
The discussion contrasts this interpretation with a possible data or quote artifact, such as a disappearing bid affecting a reported midpoint. The chart alone does not establish which explanation applies, and the alternative explanation is presented as a guess. A practical way to investigate such anomalies is to inspect trade-level records, including the trade size, reporting venue, and sale-condition flags, rather than infer significance from a chart aggregated across data sources. The document gives one example and does not establish a general rule for all sudden after-hours moves.
Key ideas
- An isolated chart spike can reflect a special trade report rather than ordinary exchange trading.
- Trade size, reporting venue, and sale-condition flags can help explain an unusual print.
- An average-price report may be connected to another transaction and may show a fractional price unavailable on an exchange.
- A quote or data artifact is another possible explanation, but the chart alone cannot confirm it.
- The example does not establish how other after-hours anomalies should be interpreted.
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# Move along, nothing to see here...just a super cheap stock price for an instant? # Move along, nothing to see here...just a super cheap stock price for an instant? Can someone explain what this large negative spike in this stock chart is in after-hours trading? It almost looks like a data glitch to me, since the value before and after the spike are almost exactly the same, but I'm wondering if it's something more significant. I occasionally see strange anomalies like this when I check a stock and it seems strange. EDIT 1 Other sources: ETradeBank: Also in this table here from NASDAQ. That page is updated dynamically, so here is a screenshot of the current data: If it's a data glitch, it must be in the primary data source that everyone else relies on. ## Answer by JoshK (score 3, accepted) https://quant.stackexchange.com/a/28253 here's a print out from Bloomberg. The trade is only 250 shares and is flagged "AP" Also, the exchange is "D", which is the ADF. That means "Average Price Trade" reported on the ADF. In English this means that this trade was tied to something else. Maybe someone had a small mistake that they had to correct for when pricing a larger chuck on TSLA options vs stock. This would just be a bit to clean it up. Also, notice the price. The fractional price is one that cannot be posted to an exchange. ## Answer by GodLovesATrier (score 0) https://quant.stackexchange.com/a/28237 I tried yahoo finance as well. The "glitch" appears there too. However all these sources get their data from the same place, the consolidated ticker. My guess is that this is just bad data, given the fact that it's out of hours, and like you say the price almost immediately corrects to exactly the level before. It might be that the mid price being reported is (say) the average of the bid and ask, and at this time the bid side disappears for a short while. Btw, when there is a proper "fat finger" error the price will move a bit more gradually back to fair-ish value often with a few trades at levels on the way down/up.
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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.