Center (American football)

The Center is usually just a bit on the short and light side for the offensive line. He'll be maybe 6'1", 295 pounds. There's a lot of people very close to him, and when the play starts they're all going to be lunging all over the place. Our center needs to fit into this crowded area and be able to work effectively in close quarters.
Before the play starts, the referees put the football somewhere on the grass. The center stands right over the football and grabs it with his left hand. He puts his right hand on the grass next to the football. When the quarterback signals that it's time to start the play, the center will sweep the ball up between his legs and hand it or toss it to the quarterback.
Just before the play starts, the center is also responsible to look at the defense and decide how the offensive linemen will protect the quarterback. The six offensive linemen have choreographed routines to use to protect the quarterback, and the center's job is to decide which routine will work most effectively against this alignment of defenders. The center knows what the play is and what the quarterback is going to try to do with the football, so he knows which parts of the field are most important. Before the play starts, you will often see the center point to particular defenders with his right hand. As he is pointing, he is also yelling out special instructions for one of the other linemen to deal with this defender. The job of the defense is to try to get to the quarterback, by pure strength, by speed, by a complicated dance of their own, or by a sneaky ambush. The center's job is to decide what the defenders are going to try this time and tell the other offensive linemen how they will try to stop it and protect their quarterback.
The center will choose between zone blocking and man blocking for each play. In zone blocking, each offensive lineman blocks an area. If a couple of defenders quickly swap places with each other after the play starts, in zone blocking the offensive linemen will just stay in their area and take on whoever tries to get through them. In man blocking the offensive linemen will slide with the defender and go wherever he goes. The very favorite of linemen is the trap block. Sometimes the play will call for a guard to move in a certain direction, leaving a hole where a defender can run right through. In this case, another lineman will "pull," meaning leave his area and run over to hit this defender. The unsuspecting defender is under the impression that he has a free shot at the quarterback, but he's about to get hit very hard from the side by a very happy 320 pound lineman.
At the very instant he starts to move the ball, there will almost certainly be a really big guy on the defense who will try to knock over the center and get to the quarterback. The center's job is to stop that guy no matter what. So we see that from about 5 seconds before the ball is snapped, that is passed to the quarterback, until about a half second after the ball is snapped, the center is the second most important guy on the offense.
Because of his job diagnosing defenses and directing other players, in addition to weighing almost 300 pounds the center is usually a pretty bright guy. Many of the best centers in the NFL went to our best universities, such as Stanford, Berkeley, USC, and Ohio State. Most of them did very well in their college classes.
As important as the center's job is, it's considered in the NFL that it's not all that hard to replace a center, so a typical center will be paid $1M to $3M per year. While this is very good money for playing a game 50 hours a year, as football salaries go it's in the bottom half.