Batter's back foot is lined up behind home plate. Coach complains

[Gre144]

Today in my game a batter had his foot behind home plate. The coach complained that he can't put his foot there because it is part of the catcher's box. Is there anything illegal about the batter having his foot not on but behind home plate? In the scenario that I am speaking of, I would imagine that if the batter's box was perfectly drawn and visible, the back foot would be mostly outside the lines of the batter's box with the heal on the chalk line of the interior side (closest to the plate) of the batter's box.

I didn't really know what to say to the coach because 7-3-1 states that the batter only needs one foot in the batter's box. With this rule in mind, it would seem to me that if one foot is in the box, it doesn't matter if the back foot is either partially or completely out of the box just so long as, that at the time of the hit, he has at least both feet partially within the batter's box(so as not to be in violation of 7-3-2)

Greg