A spread bet in tennis involves wagering on the margin of victory between players rather than simply picking a winner. In this type of bet, the sportsbook sets a line based on expected performance, indicating the number of games, sets, or points a player must win by for a bet on them to be successful. This is different from other sports where spread betting often focuses on the score difference (e.g., winning by a certain number of points in basketball or football). In tennis, spread betting is unique because matches can have varying numbers of sets or games, and the nature of individual matchups can lead to different betting lines for different players, adding a layer of complexity and strategy unique to the sport.