Spread Betting, or Point Spread was invented by Charles McNeil, a mathematics teacher from Connecticut, before becoming a bookmaker in Chicago in the 1940s. He invented the point spread as a way to make bets have a more even outcome.
The spread (or point spread) is a sports bet based on the margin margin of victory for an event. If you think Team A will win by more than 6.5 points, you have the position for Team A -6.5.
Spread betting is especially popular for those betting on basketball and football.
Underdog vs Favorite
The underdog in a spread bet will have a "+" before the margin of victory. An underdog must lose by less than the amount of points listed or win outright in order for the underdog bettor to win their bet. (see example below)
The favorite in a spread bet will have a "-" before the margin of victory. The favorite must win by more than the amount of points listed for a favorite bettor win their bet.
Examples of a spread bet: The Minnesota Vikings are favored by 6.5 points in their home matchup against the Detroit Lions. If you think the Vikings will win by at least 6.5 points , you could bet Vikings -6.5. Someone that thinks the Lions will lose by less than 6.5 points (or win outright) could bet Lions +6.5.
Unlike a moneyline bet, the odds for a spread bet do not vary as wildly (unless you are creating an alternate spread).
How is a point spread determined?
The opening line for a point spread is typically determined by oddsmakers' guess at the margin of victory between two competitors. It can range from half a point for a close matchup to 50+ points for major mismatches (like any of Alabama's preseason college football matchups). The margin of victory can move based on a variety of factors. Anything that may affect on-field performance (major injury, weather conditions, coaching changes, etc) may also affect the point spreads set by oddsmakers. In a typical sportsbook environment, the spread can move if there is a lot of action on one side. If the Vikings are favored by 6.5 points and the public is betting Vikings -6.5 heavily, the oddsmakers at a sportsbook may move the line higher (to 7 or more points) to minimize their risk. Similarly, BettorEdge markets may adjust as users create their own spreads and odds. What does it mean to "cover the spread"?
If the favorite wins by more than the spread value then they have covered the spread. In the example above of Vikings -6.5, if they win by 7 or more they have covered the spread. If they won by 4 points they would have won outright (or moneyline) but they did not cover.
If a team wins by the exact number listed on the spread, the bet is considered a push. If you have the position of Vikings -4 and they win by 4 points, your position would be returned to you (and someone that had Lions +4 would have their position returned as well). Basically, the bet never took place.
To avoid a push, the line is often set in half point increments (0.5, 1.5, 2.5, etc).