It is likely used with live betting systems(common on many gambling sites) where you can bet on the outcome of a single game of tennis. The line for the game w

It is likely used with live betting systems(common on many gambling sites) where you can bet on the outcome of a single game of tennis. The line for the game will move with each point to reflect the new situation. If a better is able to get information about points seconds ahead of the other betters, they are able to make bets on the updated odds before the line moves as the rest of the betters react to the new information. For example, consider a game with evenly matched opponents. At 0-0, the server might have odds at ~1.5, with the non-server having odds at ~2.7[1]. When the score moves to 0-15, the odds might move closer to even, eg 1.9/1.9. If you're able to get information about the first point ahead of the crowd and place a bet on the non-server at 2.7 when the true "predicted outcome" is closer to 1.9, you obviously have a massive advantage. This can also be used to bet on sets or matches, but the advantage is much smaller. Still, a better with any sort of advantage will always win over the long term. [1] Yes, those don't add up to 100%, welcome to the vig :)