“The string is out” – Why?

Listening to Tom Hamilton call the Indians game tonight made me stop and question a baseball term I’ve likely heard a hundred times. When the count was full (three balls and two strikes) Hamilton said “So the string is out.”

What, exactly, does that mean? I could Google it, but what fun is that when you can use your imagination and run with a hunch?

Years ago I read a book about settlement of the territory now known as Ohio called “The Latch String Is Out”. In pioneer days a cabin would have a latch in the inside of the door, but none on the outside. There was a hole in the door below the latch that would allow a string to loop from above the latch in the interior and out the hole. Therefore, if the latch string was threaded through the hole and left to dangle on the exterior a visitor could open the door. “The latch string is out” meant that a door could be opened.

Could this be the origin of the baseball phrase? If the count is full I would think (metaphorically) the batter has an invitation to “open the door” for a hit or walk on the next pitch.

What do you think? No fair using Google, Bing, or Duck Duck Go.