WinPicks Reference Manual
Appendix A.2. The Purpose of the Line
The purpose of the line is to make both teams look equally attractive to the gambling public. Perhaps no one would take Navy as a pick-em against Notre Dame, but Navy might look attractive to many bettors if they get Navy plus 28 points. The opening line is set by oddsmakers who try to gauge the public's opinion of the game and who want to make both sides look equally attractive. They want to balance their book, or in other words, make sure that they receive an equal amount of money on both sides of the line. The reason for this is simple -- oddsmakers don't like to gamble! If their book is balanced, they can't lose since they get to keep about 4.5% of the total amount of money wagered. If their book isn't balanced, they're gambling just like the public, and there is a good chance they could lose.
If too much money is wagered on one side of the line, the oddsmaker moves the line to encourage gamblers to take the other side. For example, if too few gamblers take Navy at +28, the line might move to +29 to make Navy look more attractive. Money moves the line. If the line is moving further and further away from Navy, you'll know that most of the money is being wagered on Notre Dame. During the week before a game, the line might constantly move. For example, it may go from 28 to 29, back to 28.5, and so on. However, the opening line seldom differs from the closing line by more than 2 or 3 points.
Sometimes it cannot be avoided, but oddsmakers try to avoid moving the line too far in the same direction. If they do, they may be middled, which means they'll have to pay out money on both sides of the line. To illustrate this, lets look at a hypothetical situation where the line on the Notre Dame-Navy game opens at Notre Dame (-27). The majority of the gambling public feels that Notre Dame will win by more than 27 points, so nearly all of the money is being wagered on Notre Dame. To entice gamblers to put money on Navy, the line keeps moving away from Navy. By kickoff, the line is Notre Dame (-32), meaning that the opening line moved by a full 5 points. Notre Dame winds up winning by a score of 40-10. This puts the sportsbook in the unenviable position of having to pay all of the gamblers who took Notre Dame and laid from 27 to 29.5 points earlier in the week, and to also to pay the gamblers who took Navy plus 30.5 to 32 points later in the week. Some gamblers may have wagered on Notre Dame early in the week and Navy later in the week and won both wagers. This is what it means to be middled. Normally a sportsbook only has to pay the people on one side of the line. In this case, they have to pay out money on both sides of the line. To avoid this situation, oddsmakers try to make the opening line as sharp, or accurate, as possible so that line movement can be kept to a minimum.
In some cases, large sums of money will unexpectedly show up on one side of the line. This isn't supposed to happen, because the oddsmakers have a lot of experience and they have set a line that (in their opinion) makes each team look equally attractive to the gambling public. Therefore, when nearly all of the money is being wagered on the same team it is sometimes referred to as unnatural money. When a sportsbook detects the presence of unnatural money, they may elect to investigate (or at least ask around) and see where the money is coming from. While they investigate, they may take the game off the board and refuse to accept further wagers. In other cases, injuries to key players or an unusual situation surrounding a team will force a game to go temporarily off the board.
As it turns out, the sportsbook industry has years of experience setting lines, and have developed an excellent feel for how the public will wager. To most people the line seems like it's about right. Normally, about half of the gamblers will like one team, and about half will like the other team. The money will usually start to fall fairly evenly on both sides of the line, which is exactly what the sportsbooks want. If the oddsmakers have done a good job of gauging the public opinion of a game and have set a good line, everything else takes care of itself. Not much line movement is necessary, the book stays balanced, and the sportsbook collects about 4.5% of the action regardless of who wins or loses. Although sports gambling has more favorable odds than almost all other forms of gambling, the odds are still against the player.
Knowing that the odds are against you, can you still beat the line? Sure. Many gamblers routinely beat the line. The key is learning as much as you can about the relative strengths and weaknesses of the two competing teams. Respect the public's perception of a game, but don't assume that it is always accurate. Do your homework and form your own opinions. The single most important thing to remember about handicapping is:
The line is based on the public's perception of the game, and not on the relative strength of the two teams.
