In the NBA, a negative spread means that a team is favoured to win a game by a certain number of points. The negative number represents the point spread, which is the number of points the favoured team is expected to win by. For example, if the Los Angeles Lakers have a -6.5 point spread against the Houston Rockets, this means that the Lakers are favoured to win the game by more than 6.5 points. If you bet on the Lakers, they would need to win the game by 7 or more points, and therefore, you will have won your bet.