Polymarket Crossed Books Explained

When the best bid exceeds the best ask, the book is crossed: a buyer is willing to pay more than a seller is asking, and the correct reading is a reprice in flight rather than an arbitrage fountain. The venue matches on the next event, and the cross is measured at 3.24% of snapshots across the corpus.

Crosses are the mirror image of one-sidedness: one side shows two-sided frenzy, the other shows one-side emptiness — both are the venue's structural texture, not errors.

Crosses form when a reference print or an event lands between quotes: an incoming bid races ahead of a stale ask, or a one-click crosses the residual. In 250ms capture, the cross is usually two or three frames wide before matching restores the book.

The measured signature: crosses cluster at reprint moments, which is why the flag matters — it marks the exact frames where price discovery was actually happening.

The archive stores the crossed flag on every row and does not filter crossed snapshots from backtests — a strategy that silently ignores them sees cleaner fills than anyone got.

Studying crosses is studying the venue's speed: the width in frames, the depth in the cross, and the reprice that resolved it are all queryable from the 250ms grid.

Crosses are information, not noise: publishing the defect flag rather than filtering is the archive's stated policy, and a cross rate of 3.24% becomes a measurable input to venue modeling instead of a mystery.

• One-sided books
• Price gaps
• Repricing data