Go back or not

[Guest Harty15]

Runner at first steals second before batter makes contact with batted ball.  Batter flies out.  Must runner who stole second return to first?

[Richvee]

Yes. He must return or liable to be put out on appeal. 1B was his base at the time of the pitch, (TOP) which is what matters. Only way he can legally stay at 2B is if he reached it before the pitcher began his motion to pitch.