The game is played by two teams, of eleven men each, upon a field 330 feet long and 160 feet wide, at either end of which are goal-posts with a cross-bar. The ball, which is like a large leather egg, is placed in the centre of this field, and each team endeavors to drive it in the direction of the opponents' goal-line, where any scoring must be done. Goals and touch-downs are the only points which count, and these can be made only as follows: A goal can be obtained by kicking the ball in any way except a punt (a certain kind of kick where the ball is dropped by a player and kicked before touching the ground) over the cross-bar of the opponents' goal. A touch-down is obtained by touching the ball to the ground behind the line of the goal. So, in either case, the ball must cross the end of the field in some way to make any score. The sole object, then, of all the struggles which take place in the field is to advance the ball to a position such that scoring is possible. A firm grasp of this idea usually simplifies matters very much for the casual spectator. The object of the white lines which cross the field at every five yards is merely to assist the referee in determining how far the ball moves at a time; for there is a rule which states that a team must advance the ball five yards in three attempts or retreat with it twenty. If they do not succeed in doing this, the other side take possession of the ball, and in their turn try to advance it. [Illustration: R. M. APPLETON. Harvard.] There are certain rules which govern the methods of making these advances, any infringement of which constitutes what is called _a foul_, and entails a penalty upon the side making it. Any player can run with the ball or kick it if, when he receives it, he is "on side"--that is, between the ball and his own goal-line. He may not take the ball if he is "off-side"--that is, between the ball and his opponents' goal-line--until an adversary has touched the ball. Whenever a player running with the ball is held, he must cry "down," and a man of his side then places the ball on the ground and snaps it back. This puts it in play, and is called a scrimmage, and this scrimmage is the most commonly recurring feature of the game. For the purposes of advancing the ball or repelling the attack of the opponents it has proved advisable for a captain to divide his eleven men into two general divisions: the forwards and backs. The forwards, of whom there are seven, are usually called rushers, and they make practically a straight line across the field when the ball is put in play on a "down." Next behind them is the quarter-back, who does the passing of the ball to one or another of the players, while just behind him are the two half-backs and the back, usually in something of a triangle in arrangement, with the last named nearest the goal which his team is defending.