Published: April 14, 2025
Parlays are often dismissed as sucker bets — and most of the time, they are. But in the hands of a professional, they can become a powerful weapon. The secret? Correlation.
In a standard parlay, the outcomes are meant to be independent. But when the outcome of one leg makes the other more likely, you have correlation. For example, if an NFL underdog covers the spread, the game is more likely to go under the total. That’s correlation — and it breaks the math that sportsbooks use to price parlays.
Most sportsbooks won’t let you parlay two legs from the same game unless they meet a “1:3” or “1:4” rule. That means the total must be at least 3 or 4 points different than the spread for the book to allow it. But sometimes this rule is loosely enforced or not applied at all — and that’s where pros look for opportunity.
Here’s a classic: in MLB, if a home underdog wins, they often do it with good pitching — and they don’t bat in the bottom of the 9th. That means fewer runs. Smart bettors parlay home underdog moneylines with the under, especially in pitcher-friendly matchups. Some books still allow this combo.
You might think betting on Connor McDavid to score over 1.5 goals and over 2.0 points is a smart parlay — but books know this and usually block it. Still, on occasion, correlated props are available. That’s when pros pounce.
Professional bettors love the final week of the NFL season. Team motivations change quickly — a team might rest starters if another team wins an earlier game. This opens the door to event-based correlation: betting Team A to win and Team B’s game to go under (due to resting starters). It’s complex, but it’s exploitable if you’re paying attention to playoff scenarios.
Most casual bettors throw parlays together for fun. Pros use them when they see a mathematical edge — and correlation is one of the best ways to find it. If you spot two outcomes that are clearly linked but the book doesn’t adjust the price, you’ve found a crack in the system. Just make sure the parlay is allowed — and bet quickly before it’s removed.