Basic Question About Center Play

[BadgerinATX]

Are centers given more leniency in terms of movement when they are making a shotgun snap or long snap versus the QB being under center? The reason I ask this is that I notice centers who are long and shotgun snapping always move their heads to see behind them and then some move their heads upward just before snapping. When the QB is under center, the center doesn't move nearly as much. If any other linemen moved their heads, they'd get flagged for a false start.

What kind of rules govern this part of the game?

 

[Beef]

Once a lineman comes set (feet in place and hand on ground) then he can not move. He can move his head and even his shoulders to look up and down the LOS, but he can not lift up his hand or move his feet.