In betting the favorite is the team that is most likely to win the game as predicted by the sportsbook, while an underdog is the team that is less likely to win the game. To understand how betting against the spread works you need to also understand the difference between favorites and underdogs. This is the way Sportsbooks level the playing field in the betting market giving both teams similar odds with a different handicap attached to the outcome. Each outcome of a points spread bet has a handicap (or a line) attached to it. When a bettor is betting on the spread it is a bet on the margin of victory. Think of this as if you are playing golf and certain players are given different handicaps to make the contest even (or as close to even as it can be) from the start. By giving each team a points/goals/runs handicap, this creates a market in which the chances of success for both teams are deemed to be even. Spread (also known as ' line' or ' handicap') is a figure set by the sportsbook to counter the perceived bias in abilities of opponents.

Betting odds and spread explained