Model vs market: projections, lines and prices
A model projection and a sportsbook line can sit next to each other and look like the same kind of number. They are not, and reading them correctly starts with keeping them apart.
The FDI projection
A projection is a model's expectation for a number — a game total, or a quarterback's passing yards — built only from information available before the game and frozen at a fixed time before kickoff. It is a model output, labelled as one.
The sportsbook line
A line is the number a sportsbook is offering at a moment in time. It reflects that book's view, the prices it wants on each side, and where demand has pushed it. It is market information, not a forecast FDI made.
The gap is arithmetic
When FDI shows a projection beside a line, it may also show the difference: projection minus line. That is simple subtraction. A projection of 265.3 beside a line of 252.5 is a gap of +12.8, and that is all it is.
A gap is not, by itself, an expected-value claim, a recommendation, or proof of any advantage. Models are often wrong, markets often know things models do not, and a large gap can mean the model is missing something as easily as the market is.
Prices and the book’s margin
A line comes with a price on each side — for example −110 on the over and −110 on the under. Those prices include the sportsbook's margin, which is why both sides of a line can carry a negative price at once. FDI shows prices as factual context; it does not convert them into a verdict.
Different books, different lines
Sportsbooks do not all quote the same number. At the same moment one may offer 45.5 and another 46.5, at different prices. FDI reports how many of the books it tracks are pricing a market and, where it summarizes a line, uses a consensus built from those books rather than picking a favourable one.
Why the timestamp matters
A quote is only true at the moment it was observed. Lines move with news, injuries, weather and demand, so a comparison between a frozen projection and a line is only fair if you know when that line was seen. That is why every market price FDI shows carries its observation time, and why an old quote is marked as not current rather than shown as if it were live.
When FDI compares a frozen prediction with the market after the fact, it uses only quotes that existed when the prediction was made. A quote from later is never treated as something the model could have known.