My DD's coach teaches leaving the 1st baseman at 1st. 2nd base covers second, SS covers 3rd, 3rd, pitcher and catcher charges bunt. Has been very effective...
We see this all the time. Lead runner on second. Batter shows bunt and the lead runner steals. The batter takes the pitch. The third baseman has left to cover the bunt. Now it's a race between SS and the runner. Tough play to make.