Batters Box guidelines

Question
In my Adult Slowpitch ASA league some batter's stand quite far from the plate, however without batter's box lines, it is not clear if they are still in the box.  Although, some stand more than a bats length away from the plate which should be clearly outside the box.  Is there any guideline for determining when someone is outside the batters box?  As a pitcher I have noticed that these batters end up running up to the pitch at an angle and often come right back up the middle.  Because they are running, if they get a good contact, the result is a very hard hit ball right back at the pitcher.  This looks like it should be a safety issue.

Answer
Hi Todd,

The box is 3' wide, 6" from the plate, so a bat length would still be in the box.  Any part of the foot touching any part of the line is considered in the box.

Is there any guideline for determining when someone is outside the batters box?
it's the umpire's judgement.

A batter can move w/in the box, they cannot step out and come back in and then hit the ball.

Mark