Because sports betting requires more skill than luck, astute gamblers and sports handicappers often find ways to beat the house. To compensate, sports books do everything possible to tilt the percentages in their favor.

The first method is charging a commission on a sports bet. Commonly referred to as the "house vigorish," the commission is usually 10 percent. This means that a bettor must risk $110 to win $100 betting football or basketball games. (If the bettor wins, the original $110 is returned to him.) In betting shorthand, the odds would be -110. The minus indicates the odds are less than 1-to-1 (technically, the are 100-to-110). If the odds were +110, then a $100 wager would return $110, and the actual odds would be 110-to-100.

Sports books also set up point spreads to make predicting the outcome of a game more difficult. The point spread is the amount of points a favored team must overcome in order for a bettor to win his bet, used mainly for football, basketball and hockey betting.

For instance, if a football team is favored by seven points, the team must win by eight or more. If it wins by less than seven points, or loses outright, the bettor loses. If the final score falls on the number, say, 21-14, it is a "push" or tie and the bet is refunded.

The flip side is that underdogs receive the points and needn’t actually win the game for the bettor to win his bet. In the above example, the underdog can either win the game, or lose by up to six points for its backers to win.

For baseball and hockey bets, the books set odds or a "money line." (For hockey, most players must contend with a point spread - usually not more than two goals - as well as a money line.)

The money line is a decimal version of betting odds (noted above in the vigorish example). It is most commonly used in baseball and hockey betting, but it is frequently offered on football bets in lieu of the point spread. Instead of listing a team as a 3-2 favorite, or a 6-7 underdog, the sports books use a plus or minus dollar figure to represent a team’s odds of winning.

A team with a negative money line is the perceived favorite and its payoff is less than the amount risked. Conversely, if a team has a plus money line, it is considered the underdog and pays more than the amount wagered.

For example, a team with a -1.80 money line means you must risk $1.80 in order to win $1 (odds of 100-to-180), which, added to your original bet gives you a payoff of $2.80. If the team’s money line were +1.80 (odds of 180-to-100), a win is worth $1.80 for every $1 bet for a like payoff of $2.80, but at a risk of only $1.

If you’re a mathematician you will have figured out that the plus money line represents odds on the underdog winning, and that the negative money line is the inverse of the odds on the favorite winning. In the above example, the odds on the underdog are 1.80 to 1, and the odds on the favorite are 1 divided by 1.80, or 0.55 to 1.

If this is as confusing to understand as it has been to write, just remember you have to bet the amount of the minus money line to win $1 (or multiples thereof), and that each $1 bet on a plus money line pays off at the stated amount.

In addition to betting on outcome of games, sports bettors can bet the "over/under," that is, whether the final score total will be either over or under a predetermined number.

During football season, parlay cards are also popular with players. The cards give players a chance to bet on a multitude of games (usually no less than three and a maximum of 10), with the chance of hitting boxcar payoffs. For instance, most cards pay at the rate of 6-for-1 for hitting a three-team parlay, and more than 600-1 for ten teams.