1st / 3rd basemen straddling the bag in foul territory

[Mista Bone]

Besides the fact that it's poor coaching, I see this all the time. I don't allow it as an umpire but I honestly can't find it in the official rule book. My belief is there have to be 8 players in fair territory when the pitch is delivered.

If this is an "illegal" pitch, what is the penalty, if any?