Under NFHS high school softball rules, a batter is called out if they contact the ball (fair or foul) while either foot is touching the ground COMPLETELY outside the lines of the batter’s box or while touching home plate. This means the ENTIRE foot has to be out of the box. If any part of that heal is on the line, your in the box.

In NCAA softball, if a batter makes contact with the ball while ANY part of their foot is touching the ground completely outside of the batter's box, it triggers a delayed dead ball. This means that your ENTIRE foot has to be in the box or on the line. ANY part of your foot out of the box violates the rule.

As you can see from above, the rules are 180 degrees different. This is why the NCAA rules committee has been trying to resolve this the last 3 years. The NCAA committee recommended going to the NFHS rule last off season, but was voted down by the full board.