A fumble in gridiron football occurs when a player who has possession and control of the ball loses it before being downed (tackled), scoring, or going out of bounds. By rule, it is any act other than passing, kicking, punting, or successful handing that results in loss of ball possession by a player.

Gridiron football, also known as North American football, or in North America as simply football, is a family of football team sports primarily played in the United States and Canada. American football, which uses 11 players, is the form played in the United States and the best known form of gridiron football worldwide, while Canadian football, which uses 12 players, predominates in Canada. Other derivative varieties include arena football, flag football and amateur games such as touch and street football. Football is played at professional, collegiate, high school, semi-professional, and amateur levels.