In sports, the "line" on a game reflects an oddsmaker's prediction not only of the outcome on the field, but also of the "action" on the game among bettors. Lines are set up in an attempt to get a roughly equal amount of money bet on both sides of each game, so that the sports book, the casino or other entity that collects and pays bets, doesn't have to pay out more than it takes in. (The book makes its profit on per-bet fees paid by gamblers.) There are two main types of sports lines: point spreads, the most common in football and basketball, and money lines, which are more common in baseball.
Identifying the type of line
Find the day's lines. Many newspapers publish sports lines, as do sports news websites. Vegas.com, a travel site operated by the parent company of the Las Vegas Sun newspaper, compiles the daily lines from all the major Las Vegas sports books.
Find the game you're interested in.
Look for the favorite and the underdog. Sometimes the favorite will actually be labeled as such. Other times, you can tell which team is the favorite because there will be a number next to it preceded by a minus sign, such as -2 or -110. If the team has a number preceded by a plus sign, such as +125, that team is the underdog.
Identify the kind of line you're dealing with. If the number following the plus or minus sign is 100 or greater, you're looking at a "money line." If it's a smaller number, usually much smaller, it's a point spread.
Reading point spread lines
Identify the favorite by the number with the minus-sign.
Find the point spread. That's the number after the minus sign. Say your game is Detroit against Chicago, and the line reads "Chicago -6." This means Chicago is the favorite, and the "spread" is 6 points.
Apply the spread. In point-spread betting, the actual final score of the game is only the starting point. Say Chicago beats Detroit 24-17. Because Chicago was the favorite, you subtract the point spread from its final score. That's the purpose of the minus sign in the spread. The spread was 6, so you take 6 points away from Chicago's point total, giving you an "adjusted" score of Chicago 18, Detroit 17. If you'd bet on Chicago, you'd have won the bet. Now, say Chicago won the game 20-17. Subtracting the 6 points from Chicago's total gives you a final score of Detroit 17, Chicago 14. If you'd bet on Chicago, you'd have lost.
Watch for "pushes." If applying the point spread results in a tie score, then the game is a "push," and all bets are refunded. That's why point spreads commonly include half-points, such as "Chicago -5.5," to make pushes impossible.
Reading money lines
Choose the team you think will win. A money-line bet is a bet on a team to win outright. You don't adjust the score; you only win the bet if your team wins on the field.
Find your chosen team's money line. Say the game is listed as "Chicago -110 Detroit +140." If you think Chicago will win, your money line is -110. If Detroit is your pick, it's +140.
Apply the money line. It's easiest to think of money lines in relation to $100. A minus sign means you have to bet that much money in order to win $100; a plus sign means that a $100 bet will return that much money. If you bet on Chicago at -110, you'll have to wager $110 in order to get back $100 (plus your original $110). If you bet on Detroit at +145, then a $100 bet will give you $145 (plus your original $100).