Line movement is the change in odds or spread from the time a line opens to when the game begins. Understanding what causes movement is essential for identifying where the value was and whether you got a good price.
Causes of line movement: 1. Sharp action — Professional bettors taking a side in size. The clearest signal of informed opinion. 2. Public action — Recreational bettors piling onto a favorite or popular team. Books adjust to balance liability. 3. Injury/news — A key player announced out can move a spread by 2-3 points immediately. 4. Weather — Rain and wind projections affect game totals in outdoor sports. 5. Scheduling — Short weeks, travel, altitude, and rest-days all impact game dynamics.
Reading movement: The most valuable signal is when a line moves opposite to public betting percentages (reverse line movement). This indicates sharp money overcoming public action.
Timing matters: Lines opened before sharp money arrives can offer better prices than lines available closer to kickoff. Early lines are less efficient; closing lines reflect the most information.
Closing line as benchmark: The closing line is considered the most accurate probability estimate. If you got a price better than where a line closed, you received positive closing line value (CLV).