A great deal of football is about deception—the offense and defense will each spend the week leading up to the game planning how to best go about neutralizing the weaknesses of their opponent. The offense, in particular, will be trying to keep the defense off balance in an attempt to gain as many yards on each play as possible or even score.
Before every play the offense decides if they will run a passing or a rushing play. Every player will know which direction the running back will run or the routes run by the wide receivers. And while the action occurs and the yards are actually gained during the play—after the ball is snapped—the team must correctly be lined up before the ball is snapped to assure that they will be able to execute the play that they have designed.
The offense has three stipulations placed on them before the snap:
- There must be seven players on the line.
- All players who aren’t on the line, other than the quarterback, must be at least one yard behind the line.
- All players must be in bounds. (I can only imagine what a team tried to pull that that rule had to be included).
Let’s take those first two a step further, what does it mean to be on the line?
- The player’s shoulders must face the goal line.
- If he is the snapper, his whole body must be behind the line.
- If he is not the snapper, his helmet must break the vertical plane that passes through the belt line of the snapper.
Just like the offense is lining up in a certain formation, the defense will be too. The defense has a little more leeway as far as their formation goes, because they don’t have requirements—like the offense must have seven guys on the line—the defense’s 11 guys can stand or move or run wherever they want to. Just because they can, and often will be moving around a lot doesn’t mean they don’t know exactly who they will be covering or where they will be going during the play.
If the offense lines up and they recognize that the defense is standing in a certain way, they can call an audible (change the play). Many quarterbacks in the NFL will audible regularly, but there’s one named Peyton Manning who has become the poster child for this over the past decade or so. During the week before the game, Manning will watch the games that the other team has played (something that every player on every team will do) and he will breakdown what they did based on the positions that they were in.
So the offense will get up to the line and Peyton will look around and if he sees something that he recognizes he will audible. Obviously he can’t just yell out, “Hey we’re gonna run the ball now!” or the defense would hear him. So he’ll use different codes and signals that only the offensive players will know the meaning of and that’s how they will know what play is going to be run. Sometimes changing to a different play will require the players to move from their current formation.
For the offense, pre-snap player movement can be achieved in two ways: a Shift or Motion.
A shift allows multiple guys to move at the same time. Maybe the quarterback got up to the line and audibled so that rather than having a receiver and a tight end on one side of the field, he wanted them on the other side. He would take a step back and call out his secret code and the players would shift. After a shift the rules say that all players must come to a complete stop and be in a set position simultaneously for at least one second.
At this point, the team can snap the ball and begin the play, or they could shift again, or they could send a man in motion.
Sending a man in motion is different from a shift, while multiple players can move during a shift only one player can go in motion at a time. If a player does go in motion though, the ball can be snapped while he is still in moving. Similar to the shift, sending a man in motion would probably be moving a player from one side of the field to the other. And if a player goes in motion and stops at his new spot, another player is free to go in motion.
The only other rule about going in motion is that the player must be moving away from or parallel to the line of scrimmage—in other words he cannot get a running start, which is something you are allowed to do in Arena Football for example.
Keep in mind that a team has the play clock to worry about, so you will rarely see a lot of pre-snap movement but you will usually see some every few plays.