Let's take this one step further - Batter in the box takes his stride with left foot and clearly steps out. LH pitcher, sharp breaking ball, breaks into batter who then turns his body away, the ball strikes the knob of the bat and rolls foul. What do you call it. Foul ball, or out for stepping out of box. It sounds rather far fetched, but a lot of the plays in the case book are far fetched as well. A good example is the foul tip that rebounds back to the pitcher.