The reason why you will typically see a (-110) line next to a point spread is simple. This is the commision in which the sportsbooks charge for you to place your wager. This is how the casino makes their money. Think of it as a commission. You make a bet, they charge 10% for you to do so. Bookmakers call this “Vigorous or Vig” it’s also known as the “Joice”

Let’s start with the basics: what do sports bettors mean when they talk about a ‘line?’ The word line, in the language of a sportsbook, can refer to either the odds and/or a point spread in any sports contest. Let’s take a look at an imaginary line the way you’d read it off the board sitting in a Vegas sports betting lounge or on the screen at your online book. Let’s imagine a game between the New York Giants and the Dallas Cowboys. Your book’s NFL betting line might look something like this:
Identify the favorite: Lines with a - before the number (i.e. -200) indicate the favorite. A -200 should be read as: "For every $200 wagered, I win $100." When there is a negative sign, the line should always be read with relation to 100. That does not mean you have to bet that much, it's just easiest to understand! When a + sign is present, just reverse the reading, always keeping reference to 100:
In North American sports betting many of these wagers would be classified as over-under (or, more commonly today, total) bets rather than spread bets. However, these are for one side or another of a total only, and do not increase the amount won or lost as the actual moves away from the bookmaker's prediction. Instead, over-under or total bets are handled much like point-spread bets on a team, with the usual 10/11 (4.55%) commission applied. Many Nevada sports books allow these bets in parlays, just like team point spread bets. This makes it possible to bet, for instance, team A and the over, and be paid if both team A "covers" the point spread and the total score is higher than the book's prediction. (Such parlays usually pay off at odds of 13:5 with no commission charge, just as a standard two-team parlay would.)
This is a huge difference. The potential profit on the moneyline wager ($143) is over 40% greater than that of the point spread wager ($100). You're a little less likely to win, as there is a chance that Seattle would lose by one or two points, but there's a more than fair chance that if they did cover they would actually win the match. And, of course, if they lost by three or more then you'd have lost either way.
That was all before Charles McNeil, a math teacher from Chicago, invented the concept of the point spread. An avid gambler, McNeil created what he called “wholesaling odds” and started his own bookmaking operation in the 1940s. He started out offering this new style of betting on football, but his business model grew to include basketball.  McNeil changed the way sports betting was done, and his legacy lives on today in what we now call the point spread.
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