The sportsbook betting sites will set an initial gambling line, whether it is developed in house or drawn from an outside source. That initial gambling line is then adjusted by the sports betting site depending on:

- Any new information or developments.
- The nature of the bets received by the sportsbook.

The sports betting sites in Las Vegas and elsewhere, are generally not looking to put their own money at risk. They want to make money from the commission they charge - the ("juice") or ("vigorish"), for accepting the sports bets. Their goal is to have a roughly equal number of bettors on both sides of any proposition.

So, If more wagers are coming in on the Chicago Bears football team to win, the sports betting site may adjust the gambling line and offer better sports betting odds for the opponent in order to encourage more people to bet on the opponent. Let's say that Chicago was favored to win and the point spread was 6. In other words, the person gambling on the opponent gets 6 points. The may increase the point spread to 9 to encourage more people to wager on the opponent.

For the sports bettor, the impact of gambling line adjustments is two-fold. First, you'll need to give some thought to which way you think the line will be adjusted.

Sometimes it is better to get your wagers in early, other times it is better to wait and see if you can get better gambling odds closer to game time. Second, the gambling line will not necessarily be the same at every sportsbook betting site. So, it is sometimes worth the effort to shop around for the best gambling odds.