Of all the types of wagers available, the over-under is unique in that it allows the bettor to go head-to-head against the oddsmaker. It is a three-step process. First, using statistics and computer calculations, the oddsmaker determines what the combined total score of a game will be. Second, the bettor decides what he/she thinks the total will be. Third, the bettor wagers “over” if his/her total is higher than the oddsmaker’s or “under” if it is lower. When successful, the payout is typically made at even money (1-to-1 odds), less the bookmaker’s commission.
In over-under betting, also known as O/U, it makes no difference which side wins and which one loses, nor does the margin of victory or defeat play a role. All that matters is the combined figure. This is most often applied to combined total scores of two teams, but it can also be used for the combined number of points scored by all teams playing on a given day, the number of wins a team will have in a full season, the speed of a tennis player’s serve, and other sports statistics.
The objective of the bookmaker is to “balance the action,” so that the amount wagered on the over is roughly equivalent to the amount bet on the under. The better the oddsmaker is a predicting the exact outcome, the more likely this will be. The initial value that is posted for betting is known as the “opening line.” Once wagers start coming in on one side or the other, the bookmaker has the option to move the line up or down to attract stakes to the less heavily favoured side.
This “moving of the line” can create some exceptional betting opportunities for the savvy handicapper. For example, if the “over” was thought to be a good bet and the line moves down, additional wagering can increase the value of winning and insure against a near miss. If the line moves up, a hedge bet can be taken on the under, creating the possibility of both bets winning if the bettor’s predicted result proves true.
Take, for example, an NBA basketball game with 186.5 as the opening line. The over wins if 187 or more points are scored. If the line moves to 185.5, an additional over bet taken still wins on 187 or more and guards against a 186 finish being a complete loser. If the line moves to 187.5, a hedge bet on the under protects the initial stake and makes it possible to win both bets if the outcome is exactly 187.
Another way to take advantage of the over-under is with in-running wagering. A bet can be placed not only on the over-under for the final total, but also on the over-under for each half, period, quarter or inning of play. Especially when the over is being bet, as soon as it success is assured, the projected winnings can be reinvested.
A good example of this is rugby. A high scoring first half can often make the over a lock. Defenses may stiffen for the next 40 minutes, making a halftime wager on the second-half under possible without sacrificing the original stake.
Other creative ways to use over-under bets are as picks within an accumulator or parlay bet, as side bets to liven up low-odds match-ups and as arbitrage bets. Oddsmakers, and particularly those at the major betting shops and online sportsbooks, have become quite proficient at setting the lines, but gaps do occur. When they do, it may be possible to take the over at one shop and the under at another and be virtually guaranteed of a profit, simply because the difference is so great.