The umpire calls a ball batted behind homeplate a foul ball. The ball spins back onto homeplate without being touched. Is the ball fair or foul?

If the ball landed behind home plate, it is already a foul ball, even if it rolls back into fair territory.

If the batter already has 2 strikes and then the ball is bunted foul, it's an out.

The above answer is wrong. If a batted ball lands behind home plate but rolls forward and settles on the plate or in front of the plate, it is a fair ball.