In this particular instance (I know the guys who ran that tennis betting syndicate), they had a tennis model that, if you told it who was about to score a point

In this particular instance (I know the guys who ran that tennis betting syndicate), they had a tennis model that, if you told it who was about to score a point, would tell you roughly what the prices in the market should move to. If you can get that "about to score" info before the rest of the market, you slam in as many bets as possible based on the reasonable chance that the market will move in the correct direction and end up getting 1.4 for something that should be 1.35. Do that all day on every tennis match you can and that's a lot of profit. You don't need spectacular statistical ability, you need minimum latency and execution skill.