What must B1 do if he is standing with his right foot outside the back line of the batter's box?

If B1 is standing with his right foot outside the back line of the batter's box, he must adjust his stance. This is important because the rules of baseball specify that a batter must have both feet within the batter's box when the pitch is delivered. If B1 is not in compliance with this rule, it could result in a situation where the umpire calls a strike or invalidates the play if the batter is not in the correct position to hit the ball. Adjusting his stance ensures that he is within the legal boundaries of the batter's box, allowing him to bat without any infractions.

It is essential for players to adhere to the rules regarding positioning, as failing to do so can lead to penalties or restrictions during the game. In this scenario, simply continuing to bat irrespective of any complaints or hitting the ball while improperly positioned is not permissible, and being automatically awarded a strike would not align with the specific rule about foot placement in the batter's box.