First time I've ever seen this:
R1 on 1st. BR hits a long high fly ball down the first base line. It looks as if it may go foul. R1 for whatever reason goes back to first in an attempt to tag and go to second if the ball is caught. He's standing there with one foot on the bag as the BR takes a big round of first base, taking about 3 steps toward second.
The wind catches the ball, and it drops in (fair) just inside the foul lines. R1 takes off for 2nd where he arrives safely while the BR returns to 1st base.
Do we have an out for a passed runner?