[UmpJM]

Rich I.,

Best I can find is the following from JEA:

Historical Notes: Umpires in the 1940's were authorized by Rule 31, Section 2 to call a balk anytime the pitcher
(1) failed to step directly before throwing to an occupied base or (2) feinted or actually threw to an unoccupied
base. The 1950 rule allowed a pitcher to throw to an unoccupied base if he were doing so for the purpose of making
a play (Same interpretation that is used today.) A casebook note was added in 1976. It clarified the issue of a pitcher
making a complete turn (without hesitating toward first base) and throwing to second when the umpire believed the
runner was attempting to advance...see 8.05 End Notes (b).

Customs and Usage: If the umpire is convinced that a runner is making a bona fide effort to advance to an
unoccupied base, then the pitcher is not guilty of throwing to an unoccupied base. See 8.05 End Notes Approved
Ruling (b).

JM