When a sportsbook makes over/under odds, the book places a line on a game that represents a total number of points scored between the two squads. To bet the over/under, you must bet on whether the actual number of points scored will fall over or under the betting total presented by the book.
The over side of a totals line is denoted with an "O" or "Over" notation, while the under betting line is designated by a "U" or "Under" notation.
For instance, in the BetMGM over/under example discussed earlier in this article, the betting total is set at 53.5. You would click on the "O 53.5" line if you wanted to bet that the combined total score between the Kansas City Chiefs and Arizona Cardinals will finish above 53.5 points. You would click on the "U 53.5" line to wager that the total will finish under 53.5 points.