Throwing to an Unoccupied Base

 
The runner (R2) is on 2nd base and the pitcher is on the rubber, in a legal set position. R2 breaks to steal 3rd base. The pitcher legally disengages from the rubber, throws to 3rd base, and easily retires  R2 at 3rd base. The coach of the offense disagrees. He claims that the pitcher balked and quotes rule NF 6.2.4b and OBR/MLB 8.05d (Wow, pretty smart for knowing that throwing to an unoccupied base is a balk).
 
3rd base was unoccupied when the play started, so is this a balk?
 
Call
While the coach is correct that it is a balk to throw to an unoccupied base, that is only half of the rule. It is a balk to throw to an unoccupied base when not attempting to put out a runner.

In the case below, there is no balk for two reasons. First, the pitcher properly disengaged the rubber, so he was no longer under the specific balk rules. Secondly, even if the pitcher had stayed engaged on the pitching rubber, R2 was attempting to advance to 3rd base, so the pitcher may attempt to retire him -- on or off the rubber.