What line movement is
Odds keep changing right up to kick-off. When the odds on an outcome fall, it usually means money has come in on it, often from professionals, or there is news: an injury, the line-up, the weather. Hence a popular idea: follow the “steam”, the rush of money that moves the price.
What history shows
We compared the sharp line's early price (a day or two before the match) with its closing price and split the outcomes into three groups: the odds fell by at least 5%, barely changed, or rose.
| Odds by the close | Outcomes | Won | Expected at the early price | Result at the early price | Result at the closing price |
|---|---|---|---|---|---|
| Fell by 5%+ | 16,381 | 33.5% | 30.6% | +7.5% | −0.5% |
| Barely changed | 43,253 | 36.2% | 35.6% | +0.2% | +0.3% |
| Rose by 5%+ | 21,411 | 27.4% | 30.9% | −14.2% | −4.4% |
- At the early price
- At the closing price
When the odds had fallen by the close, the outcome came in 33.5% of the time, against 30.6% expected at the early price. Betting on these outcomes in advance would have made +7.5%. But by the time the drop is visible, the price is different: at the close the result is −0.5% — the signal is fully priced in. Outcomes whose odds barely changed come out around zero (+0.2%).
Why you cannot just follow the move
- Where the line goes is known only afterwards. The money was made by those who bet before the move — that is, who knew something before the market did.
- Public “steam” is information that is already priced in: the odds have already fallen.
- Betting against the move is even worse: outcomes whose odds rose gave −14.2% at the early price.