In sports books, people are always talking about "lines." "What is the line on the Cubs?" "Who's hanging a line on the Michigan 500?" "That line is a crock!"

The "line" is really the single entry on the prop sheet or the board that expresses a bet that is being offered.

In the sports book (unlike race tracks), when you place a bet, it is against the sports book itself. If you can make a bet that the Yankees will win at home against the Cubs, the house is betting you they won't.

At some time before the game starts - usually well in advance of the start of the game - the house will "hang lines," that is, state what bets the book is willing to take. The "overnight line," for example, is a wager defined on the day (or night) before game day.

When you ask someone, "Do you have a line on [such-and-such]?" you are really asking for an opinion about the outcome of an event.

The house employs staff (or more likely contracts with consultants) who do detailed handicapping of sporting events so as to predict the likely outcomes of propositions. That's how the lines are set. If you want to beat the house, you have to be better than they are at predicting the outcomes of sporting events.

If the book management perceives that people are betting heavily on one side of a line, they may move it, to try to keep the house in an advantageous position.

Teams are seldom perfectly and evenly matched. Thus, the "line" will not be like a "heads or tails" proposition. They will specify the favorite and the underdog. If you want to bet on a favorite, you will have to risk more money than if you want to bet on the "dog" to qualify to take home a specific amount of money.

The two common type of lines are "spreads" and "money lines." In the example of the Cubs at Yankees, it is unlikely that there will be a "spread" line, since baseball games are often decided by just a run. Instead, the "money line" will state how much must be wagered in order to win a fixed amount (usually $100). A heavy favorite might have a money line of $200 or more, meaning that you will need to bet $2 to win $1. Spreads are common in football and basketball, and money line wagers are the norm for baseball, hockey and soccer. When there is a spread line, often the house will also put out a money line, too.

Usually, for any given contest, there will also be a "totals" line, in which the book will bet you on the number of total points, runs or goals scored in the game.

Generally the lines are organized by sport on the prop sheet and on the board.

In addition to bets on the outcomes of games or matches (spread, money line or totals), the sports book may offer other sorts of bets. They can be about an individual performer, or who will score first, or even who will win the coin toss at the beginning of a football game. Sports books might offer a bet on the outcome of political elections, or even who will win a Nobel prize. These propositions can be quite exotic, and in fact, are called "exotic props" or just "exotics." You might see an exotic that offers even money on whether the number of field goals scored by the Eagles will be more than the number of missed foul shots by Kobe Bryant in a Lakers game.

Sports books offer lines on individual competition events, like NASCAR races, tennis matches and golf tournaments. The betting structure may be a little different for these contests, but the basic betting approach is the same.

Lines change. The line listed on the prop sheet might be different from the line on the board. The board is authoritative. Sometimes the prop sheet will show an offered bet that is not on the board. This is often because the board has limited space. The prop may still be offered, but it is literally "off the wall."