With the editorial change to 10-4-4a, the basic spot is the spot of the foul for illegal batting or kicking by A that occurs behind the basic spot.
But, if the basic spot is the spot of the foul, the spot of the foul is no longer behind the basic spot, so 10-4-4a doesn't apply - so the basic spot becomes the previous spot, which then put the spot of the foul behind the basic spot, which moves the basic spot back to the spot of the foul, which means that basic spot is no longer behind....
Oh no, I've gone cross-eyed.
