What is a middle?

A potentially very profitable situation can occur in sports arbitrage and they are called middles. A middle is an arb where if a match ends with a certain result, you can either win one bet and get the other bet refunded, or win both your bets. A middle occurs when the '+' side is bigger than the '-' side (for handicap bets). For Over/Under, a middle occurs when the Over is smaller than the Under (for instance 'Over 2.5' and 'Under 3.5'). The simplest way of illustrating this is with an Asian Handicap match. Here´s an example:

$515 for Team1 (-3) 1.90 @ Bookie1
$435 for Team2 (+4) 2.25 @ Bookie2

If Team1 wins with less than three goals, you win the (+4) bet at Bookie2.
Total Profit = $28.75

If Team1 wins with more than four goals, you win the (-3) bet at Bookie1.
Total Profit = $28.50

If Team1 wins with exactly four goals, you win the (-3) bet at Bookie1. Your (+4) bet for Team2 will be refunded at Bookie2.
Total Profit = $463.50

If Team1 wins with exactly three goals, your (-3) bet for Team1 will be refunded at Bookie1 and you will win your (+4) bet for Team2 at Bookie2.
Total Profit = $543.75

Below is a graphical way of explaining a middle. This time with a basketball game, with the middle hitting (winning both your bets!) at exactly 148 points in the game. This results in a profit of around 100%

As you can see, middles could be quite profitable. If you have ample funds in your bookmaker accounts, you should bet on every middle over 0%. In some cases, it´s even profitable to place negative middles. The profit you could make if the middle hits might be worth the negative arb percentage. There are also middles in other markets.