In soccer, the ball is considered "in play" when it is within the boundaries of the field and during normal gameplay. The ball is considered "out of play" when it has fully crossed the boundary lines of the field, either on the ground or in the air, or when the game has been stopped by the referee for an infringement or substitution. Once the ball is out of play, it must be put back into play by a specific method depending on how it went out of play, such as a throw-in, goal kick, corner kick, or free kick.