If a team favored by six points wins by exactly six points, the outcome is considered a "push" and the bettors get their money back, minus the bookmaker's commission. To reduce the number of pushes, oddsmakers often set spreads with half-points. So if the Cowboys are 3 1/2- or 3.5-point favorites over the Giants, they must prevail by four or more points to pay winning bets.
Sports betting has resulted in a number of scandals in sport, affecting the integrity of sports events through various acts including point shaving (players affecting the score by missing shots), spot-fixing (a player action is fixed), bad calls from officials at key moments, and overall match fixing (the overall result of the event is fixed). Examples include the 1919 World Series, the alleged (and later admitted) illegal gambling of former MLB player Pete Rose, and former NBA referee Tim Donaghy.
That’s easy to understand because of the payouts. If a team is heavily favored, that means they’re perceived as having a better chance of winning. If that’s the case, then you would win less money betting on them. The opposite is true for the underdog: they’re deemed as having a smaller chance of winning, which means you would get a bigger payout if you bet on them (and they won).

Placing a point spread bet means gambling on how much a team will win or lose by. In our above example, the Cowboys are the favorite. How do we know that? The minus symbol in front of the point spread indicates that the bookmaker thinks the final score will have Dallas winning by 7.5 points or more. The underdog, in our example that’s the New York Giants, will always be indicated with a plus sign. If you wager on the Cowboys on the point spread, America’s Team will have to win by at least 8 points for your wager to pay off. Should the Cowboys win by less than 8 points, your bet is lost.
There are times when moneyline wagering is smarter than point-spread wagering and this is why moneylines are growing in popularity. Typically used in baseball and hockey, pro football moneylines are popular in Las Vegas for picking underdogs. The team you choose only has to win the game, not win by a certain number of runs or goals. The negative value still indicates the favorite (-150) and the positive value indicates the underdog (+130). It's easiest to picture the number 100 sitting in the middle of these two values. For example, if you want to pick a -150 favorite, you would risk $150 in order to win $100. On the underdog, you would risk $100 and win $130 if the underdog wins. It's a simple way to have the risk-reward scenario. In the right circumstance, where you have a small underdog, you can get a very similar bet by risking less and also get a bigger payout by going the moneyline route.
Point Spread: The point spread remains the favorite way to wager on pro football, regardless of how many new forms of wagering come on stream. It’s called the line or spread and it’s known as betting ‘sides.’ The common misconception is that Las Vegas sets the spread as its best guess at the margin of victory. But really, it's a number they feel that is a perfect balance and will see an equal number of people to bet the underdog as on the favorite. A negative value like -6.5 means that team is favored by 6.5 points. So deduct 6.5 points from their total score. A positive value on the same game would be +6.5 (add 6.5 points to their final score) and would make that team an underdog of 6.5 points. The favorite must win by at least seven points to cover the spread. The underdog can lose by six points and still cover.