One of the oldest and most simple forms of wagering is Sports-betting. Wagering on sporting tournaments goes back almost indefinitely into history.-
 
In Broad terms, there are 3 main approaches to winning at this form of gambling-
 
1. Handicapping
This depends on creating a statistical model of a team’s or an individual's chances in a tournament. As an example, in a game of American football you might give weightage to various factors while assessing a team's chances. You might give 1 point if the team is in good form, 3 if they are playing at home, 2 if they are playing without a star player and so on. You measure their score against the opponents and determine the chances of either of them winning.
 
Also note that this is exactly what bookies do. However, the formula that bookies use is quite unsophisticated and may not reflect the true odds (see below).

There’s a possibility to design a better model to that of the bookies. If you can design a model having a statistically considerable degree of success over the bookmaker’s model, then you will be able to recognize situations where the bookmaker's assessment of the odds is wrong and place winning wagers consistently.
 
2. Market Inefficiencies

Sometimes the bookmakers will have crazily conflicting opinions about a game. You can take advantage of this by betting with that bookmaker who is out-of-line with the consensus and offers over-generous odds. An example of this which is a bit extreme is a method known as arbitrage: this is when bookmaker’s lines overlap, so an smart bettor could bet with both and profit whatever happens.

NOTE: In practice, however, this is very difficult to do as such opportunity is quickly exploited. If the odds change before you have "closed" both sides of the wager you make yourself open to a considerable liability.
 
3. Psychology
Sometimes the bettors do not bet according to a rational assessment of their team's chances. As the most obvious example of this, in international soccer matches the home team is always heavily backed for nationalistic reasons. The resulting odds are almost always poor, while the foreign team usually has quite good odds. The bookmakers must do this in order to balance their books and get a sure profit.

Do you want to read more about Sport Betting:
• History
• Glossary