Line movement: what a moving price is telling you

§01The four reasons a price moves

Prices do not only move because someone learned something. There are at least four distinct causes, and they are indistinguishable from the outside, which is exactly why movement is a reference rather than an instruction.

• New information: team news, weather, an injury
• Money arriving: sharp, public, or both
• Operator risk management: exposure, competitor matching
• Error correction: a clearly wrong opening number

Only the first two are informative about the event. The third says something about the operator's book rather than about the match, and the fourth only says that the opening price was wrong.

A price can also be moved without any money at all. Operators copy each other, and a single significant book shortening a selection is often enough to drag the rest of the market with it — a move that reflects one operator's exposure and everyone else's caution rather than new knowledge.

§02Steam, and why the first move is the informative one

Steam is a rapid, coordinated move across several books in the same direction, usually the signature of professional money entering a market. What matters about steam is not the direction of the move but the price at which it started. The first book to move has received the money; the books that follow have received the information second-hand.

For a bettor with an estimate, this has a clear consequence: if your price is only available after the move has started, you are not taking value, you are buying at a price the market has already corrected. The edge in that situation belongs to whoever acted first.

§03Taking or waiting, priced honestly

For any estimated edge, there is a tension between taking the price now and waiting for a better one. Waiting is only rational if the expected improvement exceeds the probability that the price disappears. That comparison can be made roughly: if a price may improve by 0.10 and has a 30% chance of being unavailable later, waiting is clearly wrong when the current price already carries a positive edge.

The professional habit is to take value when it is offered rather than to optimise the last fraction of a price, because the ability to take a price at any moment is itself worth something — a bet not made cannot win.

§04Stale prices, limits and the price you cannot get

A stale price is one that has not been updated for an event the market elsewhere has already absorbed. They are rarer than they used to be and they are usually small, and they are frequently accompanied by a limit so low that the entire edge is worth a fraction of a unit. A price is only worth something if you can actually get money on it at that number.

Limits are the other side of the same problem. Operators reduce limits for customers whose bets consistently beat the closing line, because that is the observable signature of sharp play. A strategy that cannot be executed at a useful size is not a strategy, and it is worth checking what happens to your limits before you build a process that depends on a market you will lose access to.