Opening Line
Definition
The opening line is the initial set of odds posted by a bookmaker for an event. Opening lines are typically less efficient than closing lines because they have not yet been shaped by market action. Sharps often target opening lines to capture the most value.
Example
A bookmaker posts the Super Bowl total at 48.5 on Monday morning. By game time, it moves to 51.5. The opening line was 48.5 — those who bet the Over early captured three points of line movement.
Related Terms
Vig / Juice
MarketVig (short for vigorish) or juice is the commission the bookmaker charges on each bet. It is built into the odds so that the sum of implied probabilities exceeds 100%. The vig is how sportsbooks guarantee a profit regardless of the outcome.
Overround
MarketOverround (also called margin or book percentage) is the total implied probability across all outcomes in a market. The amount by which it exceeds 100% represents the bookmaker's built-in advantage. Lower overround means fairer odds for the bettor.
RTP (Return to Player)
MarketRTP is the inverse of the overround, expressed as the percentage of total stakes that is returned to bettors as winnings over time. Higher RTP means lower bookmaker margin and better value for bettors.
Steam Move
MarketA steam move is a sudden, sharp line movement caused by heavy action from professional bettors (sharps) across multiple bookmakers simultaneously. Steam moves signal strong opinions backed by significant money and can indicate genuine value before the broader market adjusts.
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