quote:8.05 CMT With a runner on first base the pitcher may make a complete turn, without hesitating toward first, and throw to second. This is not to be interpreted as throwing to an unoccupied base.
Here's a comment by Carl Childress, writing in Baseball Rule Differences, which is widely used by umpires as an aid to interpretation of the FED, NCAA, and OBR rules. 2004 edition.
"The OBR specifically informs the umpire that he shall not interpret the move as throwing to an unoccupied base. But when you fail to call a balk in FED (and perhaps in NCAA), be ready to explain yourself to the coach. Of course, the runner must be moving, not merely bluffing a steal of second."
The key here is that by turning completely to second, the pitcher demonstrates that he is trying to make a play on a runner who has already committed to second base. That's very different from a pitcher who starts to pick off at first, and decide to go to second instead. That would be a balk for feinting (failing to throw) to first.