Volume spike ("sweep")

A volume spike is an unusually large share of the day's contracts concentrated at a single strike. In flow slang this is often called a "sweep," but a true sweep — one order filled instantly across multiple exchanges — can only be identified from the trade tape.

Catalyst reads the 15-minute delayed options tape, where each sweep is detected as an order filled across multiple exchanges within moments. When one prints on a contract today we label it "Sweep" — an observed event, shown with the number of events and the dollars across them.

If the tape is unavailable we fall back to today's hourly print data (how many trades, how big each print was, and whether fills landed near the high or the low of the hour). A burst of 25+ prints — at least the contract's entire previous session — at aggressive fills is labelled "sweep-like": an inference, which is why the label says "-like."

When no live prints are available (after the close, or for a contract the intraday feed did not cover), we fall back to concentration of size and label it honestly as a volume spike. Either way, the volume number itself is always shown.