Apply the spread. In point-spread betting, the actual final score of the game is only the starting point. Say Chicago beats Detroit 24-17. Because Chicago was the favorite, you subtract the point spread from its final score. That's the purpose of the minus sign in the spread. The spread was 6, so you take 6 points away from Chicago's point total, giving you an "adjusted" score of Chicago 18, Detroit 17. If you'd bet on Chicago, you'd have won the bet. Now, say Chicago won the game 20-17. Subtracting the 6 points from Chicago's total gives you a final score of Detroit 17, Chicago 14. If you'd bet on Chicago, you'd have lost.
In our earlier example, the sportsbook would be devastated if 100% of the action came in on the Falcons. The book is not looking to gamble; they are looking for a sure thing. So, to try and entice more people to bet on the Bear Cubs and discourage people from betting on the Falcons, they will alter the payouts. They will make the amount you win for correctly selecting the Bear Cubs much larger and the amount that you win for correctly selecting the Falcons much smaller.
Sports betting has been around since 1000 B.C in China, where betting on animal fights was commonplace. In ancient Rome, one could wager on the Gladiatorial games. The idea of betting on sports is as old as organized sport itself. But up until the 1940s, bettors were fairly limited in what kind of bets they could make. The standard system of odds would allow bets on, for example, the 3-1 odds that the Steelers would beat the Browns.