Blueskyblue has probably got the picture that the feet must be wholly inside the lines before the pitch.
However I've never seen a penalty called for this violation... I, personally, have stopped play and if necessary drawn the inside line of the batter's box (6 inches from the plate) and informed the batter that he needs to start with all of his foot inside the line. I feel it is a safety issue and enforce this requirement before I allow play to continue.
Personally, I feel that this area between the plate and the batter's box is the pitcher's area to throw the ball. I don't expect the pitcher to get every pitch over the plate - there must be some latittude. In fact, a batter hit by a ball that is towards the plate from the vertical edge of the batter's box is likely not gong to get a base from me. If the batter is that confused about where he can stand, I'm probably going to call a strike. Hell, half of that 6 inches is the width of the ball.
Just my two bits... no offense TwoBits.
