The Pitch is Fouled Off

The pitcher pitches, and a runner on base takes a shot at a steal. The batter swings at the pitch, and... fouls it off.

Once the ball goes foul, it is immediately ruled dead; any runners that were in motion must go back to the base that they started from. Afterwards, you can apply the same logic here that you can apply to a foul ball where a stolen base is not involved; if the foul ball is on the ground, then everything resets immediately; if the ball is hit in the air, and stays in play, the ball can potentially be caught by the defense for an out (in which case, the runner who was trying to steal had best go and tag up). A foul bunt, meanwhile, results in a strike being added to the count, no matter what.