Definition of Move the Line

What does the term "move the line" mean in the world of sports betting? What is the definition of the term "move the line"?

The bookmaker's main goal is to set a line in such a way so that the action is spread evenly on both sides of a bet.

For instance, let's say that the Los Angeles Dodgers are playing the Boston Red Sox in baseball. The line currently looks like this:

LA Dodgers, -110
Boston Red Sox, -110

The bookmaker is hoping that an even number of bets come in on both sides. If so, the bookmaker will be guaranteed a profit, as they will collect their "vigorish".

Now, what happens if a flood of money comes in on the Dodgers because of an injury to a key member of the Boston Red Sox? Well, the bookmaker will be forced to move the line in order to compensate for the increased betting action. For instance, the line may be adjusted to look like this:

LA Dodgers, -170
Boston Red Sox, +200

In this case, the bookmaker adjusted the line in order to accommodate for the injury and the flood in bets on the Dodgers. If the bookmaker did not change the line, they would be at risk of suffering a heavy loss if the flood of bets continued on the Dodgers and LA won the game.

Note: an increase in bets is reason enough for a book to adjust a line. For instance, let's say that you walk into a Las Vegas sports book and want to bet $200,000 on your favourite team. Your bet will likely be enough to move the line.