The opening line is the first odds price published by a bookmaker when a new market becomes available. It represents the oddsmaker's initial assessment of the probability of each outcome, set before any betting action has occurred. Opening lines are particularly important in US sports betting culture, where they often appear days before the event and are widely tracked.
How opening lines are set: experienced oddsmakers (often called price-makers or compilers) use statistical models, historical data, situational factors, and their own expertise. The initial line is deliberately set at a level that the oddsmaker believes is accurate but also attracts action on both sides. In major US sports, a handful of "sharp" bookmakers set lines that the rest of the industry follows.
Opening vs closing line: the opening line is the starting point; the closing line is the endpoint after all market forces have acted. The gap between them reflects the net direction of all betting action and information flow. Sharp bettors seek to bet the opening line when they believe it is mispriced; recreational bettors often wait until closer to the event.
Early betting advantages: some markets open 4-7 days before an event. Sharp bettors who identify value early — before injury news, weather information, or roster decisions are known — can secure prices significantly better than the eventual closing line. This early access is where CLV is built.
Example
An NFL game opens on Tuesday with the home team at -3 (-110). A professional syndicate immediately bets the underdog +3, recognising the line as soft. By Friday, the line has moved to -5.5. The syndicate's early bet at +3 has achieved approximately 2.5 points of positive CLV over the closing line — a significant edge on a point spread bet.