On the play I saw yesterday, which was outside Organized Ball (Cape Cod League), the umpire took a step or two toward first base and barked something (which I couldn't make out) and the batter stopped.
It looked odd to me, but I can't say I have seen a lot of dropped third strikes mistakenly run on by the batter. The play's not dead, so I assume that wasn't what Blue was saying.
Somewhere in the back of my mind I have it that it's not proper to try to draw a throw in that situation. In that case the umpire probably went by accepted procedure.
But I looked in the MLB rulebook, which usually covers other leagues too, and the only rule I can find that pertains is this:
"Rule 7.09(e) Comment: If the batter or a runner continues to advance after he has been put out, he shall not by that act alone be considered as confusing, hindering or impeding the fielders."
The batter was out, period, because he's not entitled to try for first in that situation. Lacking any other guidance, this suggests the ump was premature to say anything.
Further thoughts, anyone?
BTW, the batter was UofM's own Terrin Vavra, playing this summer for the Cotuit Kettleers.