The one foot in rule (7-3-1) has been in fed since about 2000. Many umpires ignore it except if it starts to become a problem and actually delays the pace of the game.
Hope they aren't getting evaluated.
The rule has been in FED for at least twenty years. The penalty enforcement has changed so that it requires a delay for a penalty strike to be called. Batters are required to keep a foot in at all times unless one of the exceptions occurs, and are assessed a penalty strike if their failure to do so delays the game. Because of this, some don't enforce it until that point, which is incorrect. Keeping batters in the box before they delay the game prevents the penalty strikes from being called. I get this early in the game and tell batters to get a foot in (or to stay in if they like to wander.)