Rule 7 Section 6. The Batter is out.
D. When the entire foot is touching the ground completely outside the lines of the batter's box at the time the ball makes contact with the bat.
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This quote is taken from the fastpitch board section regarding the question of where the lead foot can and cannot be at the time of ball contact. Seems like the consensus is that the lead foot must be outside the batters box AND on the ground to be an out. In the air is irrelevant, not a violation, all ok. However, a question... the quote above states the "entire foot is touching the ground....". If there was a way to call/observe this accurately (tough to do) one could say that if the batter had the ball of their lead foot on the ground and NOT the heel then they would be legal. It is almost as if the wording was intended to really convey that the entire foot needs to be outside the batters box and some part of the foot in contact with the ground to be illegal (out). Yea, subtle difference...
Perspectives?