What is an illegal shift in the NFL?

An illegal shift in the NFL is a five-yard foul given to an offensive team who do not present a legal formation before and after a shift.

Two or more players are allowed to shift movements at the same time prior to the start of a snap. However, following the last shift in formation, all players must be at a complete stop and be in a set position simultaneously for at least one second prior to a snap starting.

Illegal shift can also be ruled if multiple backfield players are moving without the first of those to move being in a set position for at least one second prior to the second setting off.

"An illegal shift means that two players are in motion, or one is not exactly set in a fixed stance while another person is moving," former Los Angeles Chargers wide receiver coach Phil McGeoghan told The Whole 10 Yards podcast.

"It could happen on the opposite side. Some receiver could be messing with his feet 50 yards away from the other receiver going in motion and that's illegal [shift] because two guys are in motion at the same time, that's a penalty."

The rules in the NFL around offensive formations are stricter than those in lower levels of the game such as college.

While the rules are straightforward, the pressures of match situations do lead to players and teams committing the offence more regularly than they should

"If I'm a wide receiver and there's a tight end on the line of scrimmage, I must be off the line of scrimmage. So I'll check with the official, I'll point back, I give him an indicator that I'm off," adds McGeoghan.

"He'll say, okay, you're good, and then we run the play. Maybe that same receiver lines up and he covers up the tight end where he's actually on the line of scrimmage and the tight end is on the line of scrimmage.

"The tight end is illegal at that point. He cannot move down the field. Even if it's a run play, it's still a five-yard penalty.

"In the NFL, unlike college, they're very stringent about the formations and details so that the product is what you see every single Sunday. There's a lot more restrictions on your formations, your motions and shifts as there are at the NCAA collegiate level.

"Some guys get out there, they're in a panic, they're in a hurry, it's two minutes, they're dishevelled, and the simplest thing is getting lined up, but sometimes the simplest thing is not so simple."

This article is the latest from BBC Sport's Ask Me Anything team.

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