Over Under betting, or Totals as it is more commonly called, is the sportsbook predicting what they believe the total score of both teams added together is going to be. You place a wager over or under that number. Very straightforward.
Here is an example from the NBA:
Here the total expected score for this game between Houston and Dallas. Here the total set for this game is 212.5. Odds are generally, but not always, the same for one side of the the over under. In this example they are -110, regardless if you are placing a wager on the over or the under. That is the most common odd at sportsbooks. That means that a $100 bet wins you $90.91 if your bet wins. Let’s look at the score for this game:
|Houston||100||100+111= 211||← Under Winner|
In this case the score was 100 to 111. By adding those we get the actual game total: 211. That means Under bettors won with a margin of 1.5 points.
The over under or totals bet is a very interesting type of bet. You can be wrong on the winner and still win your bet on the total. Over under betting is also interesting from a human psychology standpoint because, on average, people are more likely to bet the over. The basis for this is thought to be based on the fact that there are an infinite number of scores that can make up the over, as in this example, there are only 212 outcomes that lead to a win. There is another school of thought that bettors generally don’t want to cheer for a low scoring game and therefore select the over. Sportsbooks are very aware of this fact and usually adjust the odds accordingly.