American football is played on a rectangular field, three hundred and thirty feet long and one hundred and sixty feet wide, enclosed by heavy white lines marked in lime upon the ground. For the convenience of the referee in fulfilling his duties, the field is marked by additional lines five yards apart crossing from side to side, the fifth from either end being indicated by an especially heavy one known as the "twenty-five yard line." The "center of the field" is located at the middle point of the eleventh line.

At the center of the goal lines at each end of the field two goal posts, from fifteen to twenty feet high, are erected eighteen and one-half feet apart, and connected by a cross-bar ten feet from the ground. Two "teams" of eleven men each contest in the game. Seven of them, called the rushers, or forwards, stand opposing a corresponding seven of the opposite eleven, whenever the ball is down for a "scrimmage." The one in the middle is known as the center rusher, or center, and on either side of him are the right and left guards, the right and left tackles, and the right and left ends, respectively. The four remaining players are the quarter-back, right and left half-backs, and the full-back, who stand behind the line of rushers and occupy positions which vary ac-cording to whether they or their opponents have the ball. The positions which the players will occupy when about to execute the different movements of the game are shown by the diagrams in the chapter describing the various evolutions. At the beginning of the game the ball is placed at the center of the field. The side in possession of the ball constitutes the side of attack, and endeavors to carry it down the field by kicking or running with it, in order to place it on the ground behind the opponents' goal line. The other side, forced to act upon the defensive, are drawn up in opposition, and strive to check their advance and to get possession of the ball themselves, so that they may no longer act upon the defensive, but become, In turn, the attacking party.

The rules of the game (see final chapter), place certain restrictions upon the attacking side and upon the defense, and it is the attempt made in accordance with these rules by each side to retain the ball in their possession and carry it down the field through all opposition, in order to place it behind their opponents' goal, which furnishes in rough outline the essential features of the American game of football.

Before the game is to begin the captains of the respective teams decide by a toss of the coin which side shall first be given possession of the ball. The side having the ball then places it down upon the center of the field and arrange themselves in any formation which they desire, behind the line on which the ball is placed, in preparation to force it into the enemy's territory. The side acting on the defensive are obliged to withdraw ten yards toward their own goal, and are there drawn up in opposition to await the attack of their opponents until after the ball is put in play.

As the "center rusher" of the attacking side puts the ball in play by touching it with his foot and passing it back to some other player for a run, or a kick down the field, the rushers upon the defensive side are at liberty to charge forward to meet the attack. The clash following this charge constitutes the first actual encounter of the game.

When the runner with the ball is caught, or "tackled," thrown upon the ground, and there held so that he can advance no further, he calls "down," whereupon the ball is "dead" for the moment, and cannot be carried forward or kicked until the center rusher again puts it in play according to rule.

As soon as "down" is called, an imaginary line, crossing the field from side to side and passing through the center of the ball, immediately comes into existence. Each player must remain on the side of this line toward his own goal until after the ball is "put in play," and it is one of the duties of the umpire rigidly to enforce this regulation. Should any player cross this line and fail to return before the ball is "snapped back" it constitutes an "off side play," for which the rules provide a penalty.

To again put the ball in play the center rusher places his hand upon it at the spot where "down" was called. The rushers then "line up" opposing one another, the line of attack being drawn closely together for a greater concentration of energy, while the defensive rushers are slightly spread apart to facilitate breaking through the line and stopping the advance, when the ball shall be put in play. The captain upon the attacking side then shouts some signal, understood only by his own men which indicates the evolution that he wishes his eleven to execute; whereupon the center rusher puts the ball in play by "snapping it back," that is, by rolling it back between his legs.

Immediately behind the center rusher the quarter-back has taken his stand. He receives the ball as it is "snapped back" and instantly passes it to one of the half-backs or a man in the line, for a run, or to the full-back for a kick down the field. Thereupon the first "scrimmage" of the game takes place as the opposing team attempts to break through the line and stop the play.

One side is not allowed to retain indefinite possession of the ball without making gain or loss. The rules provide that if the side having possession of the ball shall fail to make an aggregate gain of five yards, or a loss of twenty yards, in three consecutive "scrimmages", the ball shall be forfeited to the other side at the spot where it was last down.

Advances by running are made by the player directing his course through one of the six openings in the rush line, or around the ends, according as the signal may direct. The signal also indicates the player who is to receive the ball. The runner is assisted in his course by the players who border on the opening through which he is to go. These seek to enlarge the space by pushing their opponents to one side. He is further assisted by others of his own players, some of whom precede, to "block off" the opponents from "tackling" him in front, while still others follow to push him further if he is checked. The players who are to precede and the players who are to follow change with the play according as each man is enabled by his position to adjust himself to it.

Four points are scored when one side carries the ball across the goal line and makes a "touch down." The side making the "touch down" is then allowed to carry the ball out into the field as far as they may desire in a line perpendicular to the goal line and passing through the point where it was "touched down," in order that one of their number may attempt to kick it between the goal posts above the cross-bar. The other side meanwhile are obliged to take their positions behind the goal line. Should the attempt be successful, it will constitute a "goal," and two additional points be added to the score. But whether the attempt be successful or not, the ball must be delivered to the other side, who will take it to the center of the field and put it in play in the same manner as at the beginning of the game.

If the ball can be kicked between the posts and above the cross-bar by a "drop-kick" or "place-kick" by any one of the players, without having been previously carried across the goal line, it will constitute a "goal from the field," and will count five points.

In case the ball is kicked or carried across the boundary line on either side it will be "out of bounds" and must be brought into the field at right angles to the line at the point where it crossed. This is done by the side which first secures it after it passes out of bounds.

It is usual to bring the ball into the field from ten to fifteen yards and then to place it upon the ground for a "scrimmage" as from a regular down; though the ball may be passed to any one of the players, in at the point where it went out, provided that it is thrown in at right angles to the side line; or it may be "touched in" at the same point.

The game is divided into two halves of three-quarters of an hour each, and the team succeeding in scoring the greatest number of points during that time are declared the winners.

The reader should thoroughly acquaint himself with the rules in detail, before passing on to a study of the book.