3.4.15 SITUATION C:
B1 fouls A1. Just before A1 goes to the line for a one-and-one, the official observes: (a) A1 either pulls the shirt out of his/her pants; or (b) that A1's pants are partially below the hips.
RULING: In both (a) and (b), A1 will be directed to put the shirt in the pants or pull up the pants and must leave the game immediately following his/her last free throw(s). The lane is cleared and it will be B's ball for a throw-in, whether or not the last free throw is successful.
The case play doesn't include the rationale. My guess is they're tired of kids not tucking in their jerseys. They don't want to send him out, since he's due his FTs but they aren't willing to penalize the defense. If A has the arrow, you penalize B by giving the ball to A because A1 broke a rule.
I have no problem with it. Actually did it about 9 years ago. That's how I know it's there.