Batter’s Position in Batter’s Box
Rules 5.04(b)(5), 6.03(a)(1):
When the batter assumes a batting stance in the batter’s box, he shall have both feet entirely within the batter’s box; i.e., no part of either foot may extend beyond the outer edge of the lines defining the box when the batter assumes a position in the box. There is no penalty specified for violation other than the batter shall be instructed to stay within the batter’s box if brought to the attention of the umpire, or—if blatant or recurring violation—upon immediate direction of the umpire. If a player, after so directed by the umpire, blatantly refuses to comply, the player is subject to ejection. See Official Baseball Rule 5.04(b)(5).
Under Official Baseball Rule 6.03(a)(1), if a batter hits a ball (fair, foul, or foul tip) with one or both feet on the ground entirely outside the batter’s box, the batter shall be declared out. See Official Baseball Rule 6.03(a)(1).
TO CLARIFY: There are two different rules regarding the batter’s position in the batter’s box. Official Baseball Rule 5.04(b)(5) requires the batter to have both feet within the batter’s box when assuming an initial position in the box prior to hitting (no portion of the foot may be outside the line under this provision, although no penalty is prescribed other than the instructions given above).
Official Baseball Rule 6.03(a)(1) provides that the batter be declared out if he hits the ball with one or both feet on the ground entirely outside the batter’s box. (So long as any part of the foot is touching any part of the line when the batter hits the ball, he is within the rules.)