Stealing third

[Jay R]

This situation may have been discussed before but I could not find it in a search.

Ruuner on second (R2) and the pitcher comes to a set position. R2 starts to steal third before the pitcher begins his delivery. The pitcher steps towards third and throws to the 3B. R2 is now in a run down between second and third.

Did the pitcher balk? The rule book says that the pitcher can throw to an unoccupied base to make a play. The offensive coach argued that the pitcher should have disengaged the rubber before throwing to third base. Our crew said no. We said he was making a play at third. Did we get it right or did we kick it?

Jay