What happens to American odds when the point spread gets further from zero?

Question

I am learning about American odds (moneyline odds) and point spreads. In Chapter 2 of Sports Betting for Dummies, I see:

When the point spread on a game gets further from zero, the two moneyline bets get further apart. For example, they might move from -150 (on the favorite) and +135 (on the underdog) to -160 and +145.

I don't understand the example. From my intuition, when the point spread increases, the American odds (moneyline) on the favorite should increase (e.g. from -150 to -140 [and not decrease from -150 to -160 as in the example]). I don't see why anyone would accept a decreased potential profit when the probability of winning is decreased.

To give an extreme illustration, suppose the point spread increases from 0 to 1 quadrillion. To the best of my knowledge, no sports team has ever gained a 1 quadrillion point lead over their opponent, so a bet on the favorite will likely never win if there is a point spread of 1 quadrillion. Therefore, the moneyline on the favorite should increase (e.g. from -150 to +100000000000...).

Furthermore, I don't see how the first sentence is true:

When the point spread on a game gets further from zero, the two moneyline bets get further apart.

From my intuition, if the point spread is increased to a level such that the bet on the favorite and the bet on the underdog have increasingly equal probability of winning, the two moneyline bets should get closer together (and not further apart). For example, if the point spread is x, and this x point spread results in bets on both sides getting a 50% probability of winning, their moneyline should be equal (e.g. -110 and -110). Therefore, when the point spread on a game gets further from zero, the two moneyline bets get closer together before moving further apart.

Am I wrong? If so, could you explain what I'm missing?

Answer 1

I don't understand the example. From my intuition, when the point spread increases, the American odds (moneyline) on the favorite should increase (e.g. from -150 to -140 [and not decrease from -150 to -160 as in the example]). I don't see why anyone would accept a decreased potential profit when the probability of winning is decreased.

The spread increases when the game is predicted to be more lopsided. The favorite is now more favored. The chances of the favorite to win are perceived to have increased, so the moneyline payment for their win goes down.

so a bet on the favorite will likely never win if there is a point spread of 1 quadrillion. Therefore, the moneyline on the favorite should increase (e.g. from -150 to +100000000000...).

Ah, here we go. Moneyline and spread are different bets. Spread bets are almost always priced at -110/-110, but the favorite has to win by more than the spread. Because this pricing is standard, it's not usually shown. Moneyline bets are for the team to win outright (no spread), but with different pricing.

In your example, the moneyline bet will pay out a small amount of money to a lot of people if the favorite wins, but the spread bet will pay a lot of money to folks on the underdog when the favorite doesn't cover.

Answer 2

Maybe it's helpful to explain in a different way. Remember how the moneyline works: -150 means "You have to bet $150 to win $100", and -160 means "You have to bet $160 to win $100". Both bets, though, are on a "straight up" win - the team that gets the W in the standings wins the moneyline bet.

Let's say we have a game between the Dogs and the Cats.

• Initial spread: Dogs -4 (-110/-110)
• Initial Moneyline: Dogs -150 / Cats +130

Here, it is saying that you can:

• Bet $110 on either the Dogs or the Cats to win $100, with a -4 adjustment to Dogs' score
• Bet $150 on Dogs to win to get $100, straight up
• Bet $100 on Cats to win $130, straight up

Now, let's say the Cats star player gets hit by a car and is out for the game. Clearly, the line will move in the Dogs' favor (assuming they don't withdraw the game from betting).

• Updated spread: Dogs -6 (-110/-110)
• Updated moneyline: Dogs -180 / Cats +150

Now, if you bet on the Dogs straight up, you have to put forward $180 in order to win that $100, and you get $150 for your troubles if you bet on the Cats to win straight up. Basically, moving the moneyline further apart means you get less money from betting on the favorite, and more money from betting on the underdog, which makes sense when the spread is increasing - that means the favorite is more favored, and the underdog is less favored.