11) He fails to return at once to first base after overrunning or oversliding that base. If he attempts to run to second he is out when tagged. If, after overrunning or oversliding first base he starts toward the dugout, or toward his position, and fails to return to first base at once, he is out, on appeal, when he or the base is tagged;
Rule 5.09(b)(11) Comment: Runner who touches first base in overrunning and is declared safe by the umpire has, within the intent of Rule 5.08(a) "reached first base" and any run which scores on such a play counts, even though the runner subsequently becomes the third out for failure to return “at once,” as covered in Rule 5.09(b)(11).