An over–under or over/under bet is a wager in which a sportsbook will predict a number for a statistic in a given game, and bettors wager that the actual number in the game will be either higher or lower than that number.
The Over/Under soccer betting markets enable punters to bet on over or under a particular number of goals to be scored in a game, without the need to be specific about the scoreline. The most popular line is “Over/Under 2.5 goals” — but there’s also 1.5, 3.5 and so on.
The reason the Over/Under markets are listed with decimals like 2.5 rather than whole goals like 2 is that in this way all possible scorelines are included. For example, in an “Over/Under 2 Goals” market, a 1-1 draw would be disregarded entirely as it has neither over nor under 2 goals; it has 2 goals exactly.
Now imagine you place a bet on “Under 2.5 goals” in a match between Everton and Leicester. In this market, the scorelines of 0-0, 1-0, 0-1, 1-1, 2-0, and 0-2 are all winning outcomes (as they each have less than 2.5 goals). For any other outcome, the bet is lost — it’s as simple as that.

With tennis betting, it will be total games of the match

With basketball betting, it will be total points of two team