Fair and Foul Balls

General notes:

The position of the fielder's body or feet, have absolutely nothing to do with judging whether a ball is fair or foul. The judgment is based solely upon the relationship between the BALL and the LINE at the moment the fielder touches the ball, or at the moment the ball comes to a stop, or on outfield fly balls; the moment it touches the fielder or the ground.

Batted balls that go in-flight from the bat and first touch the ground in the outfield (fly ball to the outfield), are judged a bit different from batted balls that go from the bat and first touch the ground in the infield, before reaching first or third base (ground balls.)

Home plate is irrelevant. Home plate is in fair territory, but other than that, it is just the same as the ground. A ball that hits the plate first, or ends up on the plate, is no different from any other batted ball.

OUTFIELD FLY BALLS

An outfield fly ball is judged to be fair or foul by the relationship of the ball to the foul line at the moment it first touches the ground, or where it first touches a fielder. If the ball touches a fielder in-flight, the judgment is made at where the ball was when it was touched, NOT from where it may land after a miss, or drop of the ball, by a fielder. The position of the fielder is irrelevant. You only focus on the ball and the foul line.

INFIELD GROUND BALLS

Ground balls  that bound between home and first, or home and third are a little tricky. The ball is not ruled fair or foul, until the ball comes to a stop, is touched by a fielder, or goes past first or third base.

The ball may zig-zag, back-and-forth, between fair and foul ground an unlimited number of times. The ruling of fair or foul is not made until the ball finally comes to a stop, or is touched, or goes past first or third base.

THE ACTUAL RULE from the rule book

A FAIR BALL is a batted ball that settles on fair ground between home and first base, or between home and third base, or that is on or over fair territory when bounding to the outfield past first or third base, or that touches first, second or third base, or that first falls on fair territory on or beyond first base or third base, or that, while on or over fair territory touches the person of an umpire or player, or that, while over fair territory, passes out of the playing field in flight.

A fair fly shall be judged according to the relative position of the ball and the foul line, including the foul pole, and not as to whether the fielder is on fair or foul territory at the time he touches the ball. If a fly ball lands in the infield between home and first base, or home and third base, and then bounces to foul territory without touching a player or umpire and before passing first or third base, it is a foul ball; or if the ball settles on foul territory or is touched by a player on foul territory, it is a foul ball. If a fly ball lands on or beyond first or third base and then bounces to foul territory, it is a fair hit.

EXAMPLES:

Watch this video that is from the DVD that can be purchased here on this site

Fair or Foul Ball Video

Foula

The ball above is a fair ball.
If ANY part of the ball is over the chalk line, the ball is ruled as FAIR.

Foulb

The ball above is a fair ball.
The batter's box is irrelevant as far as judging a batted ball that does not touch the batter while he is in the box, or any fielder.
If the ball stops untouched as in the picture above, the ball is FAIR.

Foulc

The ball above is a fair ball.
The plate is in fair territory.
The foul lines run from the back point of the plate, toward first and third.