Steam moves — what they are, and why chasing one rarely works

What separates steam from ordinary movement

Lines drift all week. A steam move is different in two ways: it is fast — minutes, sometimes seconds — and it happens across many books at once rather than at one.

The simultaneity is the tell. One book repricing is that book's opinion. Every book repricing together means the same information, or the same money, arrived everywhere at once.

What causes one

Sometimes news: a late injury, a lineup scratch, weather at an outdoor venue.

Sometimes coordinated wagering — the same position taken at many books in a short window, which the books notice and respond to together.

From outside you frequently cannot tell which, and the distinction matters less than it seems, because either way the price has already changed.

Why chasing it does not work

By the time a steam move is visible on a screen you are looking at, it is finished. The number you can now bet is the post-move number — you are taking the worse side of the adjustment that just happened.

This is the same structural problem as any publicly visible signal. If you can see it for free and instantly, so can everyone, and the price already reflects it. The move is real; the opportunity is not.