The point spread bet does not depend entirely on the victory of a team.
A bettor is considered to win the bet only if his team wins with a predefined victory margin. The victory margin that the favorite team is expected to get is decided at the time of betting. The technique is often called covering the spread. The bettors that support the underdogs can win the bet even if they loose. If the favorite team win with point less than the victory margin quoted at the time betting he will get his amount. Normally the quoting is based on $100. A better have to put $110 for winning $110. The margin of $10 is the commission for the bookmaker. This type of betting is often seen in basketball or American football.
Consider a football game between the Hunters and Dallas, and Hunters are considered as a 30 point favorite. This will be quoted as Hunters -30 or Dallas +30. If Hunters defeats Dallas for more than 30 points, the bettors who supported Hunters is considered to win and will get $100 and loser will loose all the $110. If Dallas wins their bettors will get $100 and Hunters will loose their money. If the Dallas loose the game for less than 30 points the Hunters preferred bettors will still lose their money and the Dallas bettors will be benefited.
But if the Hunters wins by an exact 30 point lead neither of the bettors are considered to win.
The general practice in United States is that the full amount will be returned to the bettors. This is called push, t avoid this bookmakers often set the spread which include half a point. This will help the bookmakers from loosing their commission.
Another point spread method is in predicting the total score earned by both the teams. Such type of bettors is called totals over or under. For example in a football game we looked into above between Hunters and Dallas may score over a total of 60 points. The bettors can stand either on the over side that is above 60 or under side below sixty. The bookmakers may set the spread point as 60.5 to avoid pushes.