any ball that is in play and not in a player's possession. This includes a ball in flight during a lateral or forward pass.
a ball that is not in possession of either team, such as after a fumble or a kickoff; it can be recovered by either team.
A ball that is alive but not in the possession of either team.
A situation in which neither team has control of the ball.
a ball that is in play; but is not in possession of either team.