The Batter's Box

Feedback has suggested the wording in the Guides could be clearer.
(Thanks Nick - Meteors 3)

"At the time the batter makes contact with the ball, both feet must not be completely outside the box..."
or maybe
"At the time the batter makes contact with the ball, neither foot can be completely outside the box..."

It doesn't matter if the ball is hit fair or foul, the batter is out if one foot is completely out of the box on contact. A foot in the air is allowed (but probably something your coach or team mates will tell you is not how to bat!)
Rule 6 Section 6d

But hold on...
What do Umpire's do about pitches where there are no batter's boxes marked out? (Finsbury Park for example)
First off tell the Captains what you plan to do along with other ground rules.
It becomes a matter of judgement but the foot will need to be obviously far outside the imagined box to reasonably call someone out. Warnings and a quiet word will keep players in line.