In baseball, the rules state that a batted ball is considered in flight when it has not yet touched any object other than a fielder or his equipment.

Thus, once a batted ball touches the ground, a fence/wall, a base, the pitcher's rubber, an umpire, or a baserunner, it is no longer in flight. A batted ball that passes entirely out of the playing field ceases to be in flight when that occurs.

If a batted ball is caught in flight, the batter is out—called a fly out—and all runners must tag up. A batted ball cannot be ruled foul or fair while in flight; a batted ball that is past first or third base will be called foul or fair based on where it ceases to be in flight, or where it is first touched by a fielder, whichever occurs first.

If a batted ball passes out of the playing field in flight more than 250 feet (76.2 m) from home plate and is fair, it is an automatic home run, entitling the batter and all runners to score without liability to be put out.