What causes sports betting odds to change?

Injuries aren’t the only things that move betting lines.

Much like the stock market, viewing a sports betting odds screen can feel overwhelming for casual and advanced bettors alike. With the odds constantly changing across a variety of sports, the odds screen can light up like a Christmas tree – especially at certain points of the week, like on Sunday morning during an NFL season.

There are a variety of different markets that sportsbooks operate, from a moneyline to a prop bet to an over/under to a point spread. The common theme, though, is that these odds shift from the time a market opens (“the opening line”) to when the market is closed because the game is about to begin.

But why exactly do oddsmakers change the odds? What are they reacting to?

If we take the NFL as an example, there are two main factors: injuries and respected action.

In the NFL quarterbacks are obviously the most important players. A starting quarterback such as Patrick Mahomes can be worth as many as seven points more than his backup against the spread, meaning that if Mahomes was ruled out, the line could shift seven points away from Kansas City in a game.

For example, if a game was Chiefs -6 on the lookahead line and then Mahomes sprained his ankle and was questionable for the following week’s game, it may re-open at Chiefs -5.5, -5 or -4.5 at some books, just in case he doesn’t play. And once the news came in at any point that he was ruled out, the line would shift significantly, likely to around a pick ’em or the opponent favored (depending on the team).

“Line moves can happen on any sport if a player is injured or ruled out that they’re not playing,” Thomas Gable, sportsbook director at The Borgata in Atlantic City told me. “A player is worth something to every number. Injuries, rest days, those all move the number.”

The other reason is a respected bettor making a wager in a market. You often hear about “sharps” in sports betting media, but there are very few professional bettors that exist and even fewer that are respected by sportsbooks. If a respected bettor makes a small wager on a game, oddsmakers move the line in response – even if a public bettor wagered much more on the other side (or even the same side).

“The other thing that moves the number [is] who is making the bet” Gable told me. “I always use this example, it could be an NFL Sunday and I could take a $300,000 wager from a casino guest and we don’t move the number. It’s simply because we know who that person is, they’re just taking a shot at the game. Someone we respect may come up and make the same wager for $5,000 or $10,000 and we will move the number off that bet.”

Weather will also move numbers, specifically totals, depending on if it’s cold, hot or windy, or if there is some form of precipitation. Obviously, in indoor sports like the NBA, this doesn’t apply.

Another reason for some smaller operators to move the odds is to stay in line with the market and move off of books that cater to sharper bettors. One oddsmaker told me that he will keep an eye on certain sportsbooks like Circa Sports or offshore books to see if they move on a game – and will react accordingly. Because there are certain books known to take action from sharp bettors (and some that don’t), it’s valuable information for other sportsbooks to see those lines moves, as it’s likely where the market is heading. For example, if FanDuel Sportsbook is at Chiefs -4.5 and Circa, an offshore book and a few other sharp books are at -5, it’s worth “moving on air” to Chiefs -5 to be in line with those books.

Sometimes, sportsbooks shift the odds based off existing liability or money coming in. For example, let’s say the Minnesota Vikings were playing the Detroit Lions in Detroit and the line was Lions -6. If a sportsbook had received 80% of bets and 90% of money on the Lions to cover, it may shift the odds (to say, Lions -7) in order to attract money on the other side. Sportsbooks are willing to “gamble” a bit with an opinion on a game, but everyone has bosses and sometimes executives upstairs wondering about the total potential loss on a game aren’t comfortable if it’s too big.