A middle is a situation where line movement creates an opportunity to bet both sides of a point spread at different numbers, giving you a chance to win both bets if the final margin lands between the two numbers.
Classic middle example: You bet Team A -3 early in the week. By game time, Team A is favored by -5.5 at other books. You bet Team B +5.5. If Team A wins by exactly 4 or 5 points, you win both bets. If Team A wins by 3 (your original line) or 6+ (covering the +5.5), you win one and push or lose one.
Middle math: The value of a middle depends on the probability of the score landing in the middle range and the vig paid on both bets. A 2-point middle in football (one of the most common final scores) has roughly a 7-8% hit rate — making it valuable if the vig is manageable.
Scalp vs. middle: A scalp (arb) guarantees profit regardless of outcome. A middle doesn't guarantee profit but offers a chance to win both bets. The EV of a middle includes the probability of the middle hitting.
Finding middles: The Shark Snip team odds page highlights current middle opportunities across games where odds_snapshots show divergence between books on the same game's spread.