Un-noticed Fair Ball

[bniu]

I had this happen once. Right handed batter dribbles one on the plate, ball comes to rest in the upper corner of the other batter's box in the fair territory part, and catcher picks it up, she had no clue what to do, but she threw down to first to try to nab the runner on first who was leading off (no clue why she would do this if she felt it was foul...)
This whole time, IM pumping my arm fair
first baseman takes the ball while off the bag, does a casual tag on the runner and "accidentally" steps on first afterwards with the ball. Batter-runner is still at home plate, I announce loudly, "double play!".

Coach comes out asking why a hit ball landing in a batter's box can be fair, and I point to where the ball was, he takes a look, and realizes his mistake. He figured the rest of the play out on his own. Earned a lot of cred with the coach, he ended up calling me to call a bunch of his games later on...