With a runner on 2^nd base, the batter bunts a fair ball down the first base line in order to attempt to move the runner over to 3^rd base. The first baseman fields the bunt, but as he attempts to tag the batter-runner, the batter-runner begins to retreat towards home (in order to give his teammate more time to advance to 3^rd base). The umpire calls the batter-runner “out” as soon as he begins his movement back towards home. Is that the right call? Can a batter-runner go back towards home before he reaches 1^st base?