In modern American football, the quarterback is usually considered the leader of the offensive team, and is often responsible for calling the play in the huddle. The quarterback also touches the ball on almost every offensive play, and is the offensive player that almost always throws forward passes.
The offensive line, or O-line, are the group of offensive players that play up front and block for the quarterback and running backs. Even though the quarterback and running backs get all the glory and press, they couldn’t do anything without the offensive line.
Running backs line up in the offensive backfield with the quarterback. They are the primary rushers on the team. They also catch short passes and provide extra blocking.
Receivers are offensive players who specialize in catching passes downfield. They are often some of the fastest players on the field. Receivers come in all sizes from small players well under 6′ tall to tall big players over 6′ 5″. The smaller players excel due to quickness, speed, and running precise routes. The larger players are able to out jump smaller defenders and present a big target for quarterbacks.
The defensive line makes up the first line of defense. They are responsible with stopping the run and rushing the quarterback.
Linebackers play in the middle of the defense between the defensive line and the secondary. They must do a little bit of everything from stopping the run to pass coverage to rushing the passer.
The last line of defense in football is the secondary. The secondary covers receivers downfield and tackles running backs who make it past the linebackers. Players in the secondary are generally small, but very fast.
The kickers are members of the special teams in football. They have very specialized skills and roles to play in the game.