In flight

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.

Once a batted ball touches the ground, a fence or wall, a foul pole, 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 it was between the foul poles at that moment, then it is a home run which entitles the batter (and any other runners on base) to score.

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 and is fair, it is an automatic home run, entitling the batter and all runners to score without liability to be put out.