Fielding Yost, Football for Player and Spectator… (1905)
“ At least six men of the side holding the ball must be on the line of scrimmage. If not more than six men are on the line of scrimmage one man of those not on the scrimmage line must be outside the position occupied by the man on the end of the line. The line of scrimmage is an imaginary line parallel to the goal line and passing through the front point of the ball. A player shall be considered to be on the line of scrimmage if he has his head, his foot, or his hand up to or within one foot of this line. He must also, however, be outside the player next and between him and the snapper-back. ”
