Ever wondered why lines move?
Sportsbooks are quick to adjust off of information.

What Is Line Movement?

The term “line'' or "lines" is used often in sports betting. Lines refers to either a specific line such as a point spread or total (over/under) or the odds (price) of a bet. These lines will undoubtedly shift between the time when they are released by a sportsbook, right up to game time.

There are a number of reasons that betting lines move, but let’s begin with the most obvious.

Generally speaking, sportsbooks aim to have close to an even amount of risk (action) on both sides of a bet. This means regardless of the outcome, the sportsbook will make a profit on the result based on their commission (also known as vig), which is what they charge the bettor in order to place the bet. Now this is not a 100% rule of thumb as sportsbooks often don't mind to have liability on one side of a game, but more often than not, they are looking for balanced action.

If the sportsbook begins to take an abundance of action on one side of a bet, they will adjust their lines accordingly in an effort to balance their action. By making the opposite side of the bet more attractive (bigger payout or better line), it will entice more bettors to put action on that side. The lines are altered in one of the following ways:

  • A change in the point spread (for example from -6 to -7)
  • A change in the game total (for example from 48.5 to 49.5)
  • A shift to more valuable odds, such as a higher payout on the money line (for example from +190 to +200)

What Other Factors Can Move a Line?

We've already discussed how the sportsbooks shift the lines to minimize their potential risk. Other factors which could move a line include:

  • Injuries
  • Suspensions
  • Weather
  • Pitchers, goalies, or other player scratches

If a key player suffers an injury (or illness) that will keep him from competing (for example a starting quarterback) the sportsbooks will adjust their lines to reflect this information. This can often happen because the sportsbooks themselves would see a rush from bettors to bet one side or outcome of the game.

For example, in Week 7 of the 2021/22 NFL Season, The Kansas City Chiefs opened as a -115 favorite against the Green Bay Packers. When news came out that Packers quarterback, Aaron Rodgers, was going to miss the game due to Covid-19, the line quickly moved and Kansas City was then adjusted to a -350 favorite. This is an extreme example of a line movement, but it does happen.

Weather can also play a role in the outcome of a game. For example, in football, if there is a forecast of high wind, the game is likely to produce fewer points. With this information, bettors would be lining up to bet the under and bookmakers would then react by reducing the total (over/under) of the game. 

Some coaches may decide to scratch (not play) a player before the game. Coaches may do this for a few reasons:

  • To rest the player
  • Because the player has fallen ill
  • The player has not been playing well

If this were to happen to an important player, the sportsbook would undoubtedly make an adjustment to their lines. A greater shift in the line would involve the absence of key players at key positions. The starting quarterbacks, goaltenders and pitchers are among the most notable.

Sharp Money

Online sportsbooks are well aware of their customers, and their betting history. As a result, they know which accounts are likely to belong to “sharps” (professional bettors). The sharps typically place higher volume bets, and have a larger bankroll in their accounts. Since the sharp players are more likely to be profitable, the sportsbooks will often adjust lines to limit the amount of wagers that are following the sharp money.