Spread betting was invented in the United States in the 1940s to inject interest into one sided sporting events. For example if one football team is an overwhelming favorite to win a game it would not generate significant wagers. Bettors would not want to wager on the underdog because it was unlikely to win. And Bettors would not want to wager on the favorite because the odds offered would be very unattractive.
Spread betting overcomes this by allowing players to wager for or against a given margin of victory. The margin is so chosen that the contest becomes even. It is most popular in American football and all USA betting sites offer spread betting. Bodog.com is one such online betting site and spread betting will be explained using an actual bet offered by it. On Wednesday January 5 there is a football game between Ohio State Buckeyes and Arkansas Razorbacks in the NCAA Bowls. The spread for the Buckeyes is -3.5 (19/20) and that for the Razorbacks is +3.5 (7/8).
The first thing to note is that the minus sign for the Buckeyes indicates that they are the favorites, while the plus sign for the Razorbacks indicates that they are the underdogs. If a bettor wagers on the Buckeyes then that team would have to win by more than 3.5 points (practically 4) in order for the bettor to win his bet. If a bettor wagers on the Razorbacks then that team would have to lose by less than 3.5 points (practically 3) in order for the bettor to win his bet. The bettor would also win his bet if the Razorbacks won the game despite being underdogs.
Ideally each bet, if won, would be paid out even money. However, the sports betting site has to earn something to cover its costs. There fore the actual payout is less than even money. The odds are indicated within the brackets. A player wagering on the Buckeyes would win $19 on a wager of $20, assuming that his wager wins. A player wagering on the Razorbacks would win $7 on a wager of $8. Usually a larger commission is charged from the bet for the favorite team.
Bettors are advised to understand spread betting completely and to compare odds at different betting sites before placing wagers.