The goal of an offense in American football is to score as many points as possible against the defense of the opposition team. The offense uses 11 players at a time, though the combination of positions may vary from play to play. Here is an introduction to the most common positions on an American football offense.
The quarterback lines up behind the center of the offensive line. He is the primary passer on the team. He may also run the ball if he so chooses. There is usually only one quarterback on the field at a time. He may change the play at the line of scrimmage, order the receivers to run different routes or change blocking assignments based on his assessment of the defensive lineup. For these reasons, the quarterback tends to be considered the leader of an offense in American football.
The running back is the primary runner on a team. He usualy lines up somewhere in the vicinity of the quarterback in order to receive a toss, pitch or handoff. He may also catch the ball. There are usually 1 or 2 running backs on the field at a time, but some formations may require more. Other names for this position include halfback and tailback. These words are somewhat interchangable.
The fullback has most of the responsibilities of the running back but may also be called to block for an American football team. They tend to be stronger and have larger builds than the average back. Due to their size fullbacks are harder to tackle and may be called upon to run the ball in short yardage situations and near the opponent's endzone. They line up near the quarterback and running back, when applicable. Typically there is only one fullback on the field at any given time.
The offensive line consists of five players. They set up on the line of scrimmage and their responsibilities are to block for the passer or anyone else that possesses the ball. There must always be 5 of them on the field at a time. Positions within the offensive line are, from left to right: left tackle, left guard, center, right guard, right tackle. The center is responsible for snapping the ball to the quarterback. The tackles guard the edges. The guards are positioned between the center and the tackles.
The tight end in American football is a versatile position that requires some blocking skills as well as some receiving skills. Thus tight ends tend to be smaller and more athletic than linemen but larger than the smaller and quicker wide receivers. In passing situations there tends to be anywhere from 0-2 of them on the field. In running situations there can be as many as 3. They are called for more on a running play because of their blocking skills. They may also be present in passing situations to set up a play action pass.
The wide receiver is the primary pass catcher in American football. There may be as many as 5 wide receivers on the field at a given time. They are some of the the speediest and most athletic members of a team.