Instead of just picking which team wins, spread betting asks you to predict how much they win or lose by.
The sportsbook sets a number called the "spread" based on how mismatched the two teams are. The favorite gets a minus number (they need to win by more than that amount), and the underdog gets a plus number (they can lose by less than that amount and your bet still cashes).
Both sides of a spread bet typically have similar odds, usually around -110, so you don't need to risk a fortune backing a heavy favorite like you would on a moneyline.
Spread betting is also called "handicap betting" in soccer and European markets, or "betting against the spread" (ATS) in American sports. The mechanics are the same.
The .5 you'll see on most spreads (like -6.5 or +3.5) exists to prevent ties. You can't win by half a point, so there's always a winner. When the spread is a whole number and the margin lands exactly on it, that's called a "push" and your bet gets refunded.
Spreads vary by sport. NFL spreads typically range from 1 to 14 points, with 3 and 7 being key numbers. NBA spreads can stretch past 15 points. Soccer spreads are much tighter (usually -0.5 to -2.5 goals). In esports, you'll see map spreads like -1.5 in a best-of-3.
BlockBet covers spread betting across 60+ sports and esports, from Premier League soccer to NBA basketball to Valorant.