How Sports Betting Works

What Are the Odds?

Bets are placed on football (both legally and illegally) at all levels of the game, from the Super Bowl to high school playoffs.
Bets are placed on football (both legally and illegally) at all levels of the game, from the Super Bowl to high school playoffs.
Photo courtesy John Pilge, MorgueFile

The point spread for a football game or the money line for a baseball game are both referred to as "the line." The line is simply the odds for that particular game, translated into whatever system is used. When a big Las Vegas casino issues the first line on a game, it is known as the "opening line." Offshore sports books often issue a line before Vegas does, but the Vegas line is usually considered the most trustworthy.

Setting the line is a matter of intense research, carefully cultivated contacts, years of experience and plain old intuition. An oddsmaker's reputation is based on his accuracy, and he has many variables to consider when determining the odds:

  • The teams' performances this season, in prior seasons, in last week's game, and against each other
  • The playing surface
  • Home field advantage
  • The weather forecast
  • Injuries, especially those of star players
  • Team morale
  • Events in the personal lives of the players

Oddsmakers don't try to predict the outcome of the game when setting point spreads. If a team is favored by seven points, that doesn't mean that the oddsmaker necessarily thinks it will win by seven points. The oddsmaker's goal when setting the line is to keep an equal number of bets on both sides of the game. The betting public's perception of the game can be as important as the actual comparison of the two teams.

Why do oddsmakers try to keep the action even on both sides of a bet? A bookie's worst fear is being "sided." This happens when many bets come in on one side of a game. If that side turns out to be the winning side, the bookie will lose a lot of money. Ideally, half the bettors lose, and their money goes to pay off the other half, who won, with the bookie taking the vig.

Oddsmakers are so intent on keeping the action even that they actually move the line in response to betting patterns. If too many bets are coming in for the underdog, then that team might have been given too many points, so the line is moved. Bets made prior to the move are still counted at the old line. Some bettors will make additional bets after the line moves, on the opposite side of the game. This is known as middling. For example, let's say the opening line on a football game is Tampa Bay -7; SAN FRANCISCO. A lot of people might think Tampa Bay will beat San Francisco by more than seven points, so they all bet on Tampa. The oddsmaker sees this pattern and moves the line, giving Tampa -10. Now, Tampa has to win by more than ten points for bets placed on Tampa to win. A bettor can place another bet with the new line, this time on San Francisco. If Tampa wins the game by eight points, the bettor has middled -- he's won on both bets.

Sometimes a single well-known gambler can force oddsmakers to move the line. When one of these gamblers makes a bet, a lot of people pay attention and bet the same way, because he has a reputation for winning frequently. This can draw so much action to one side of the bet that the oddsmaker must move the line.

Often oddsmakers will move the line independently of the Vegas line in response to local betting patterns. Over time, they gain experience in setting the odds themselves. If they develop a reputation for setting accurate lines, they might be hired by one of the Las Vegas casinos, the only places that can legally hire oddsmakers in the United States.

Next, we'll check out the history of betting on sporting events.