When the ball is snapped, no player may be advancing toward the line of scrimmage. All other players must remain in their spots at all times. If an eligible receiver on the line goes to a different position on the line (other than forward), he must reset before the snap. It is an unlawful motion if he does not reset. For example, if a back moves laterally across the line after the snap, that is a violation. The exception to this rule is when a team wants to get a free rusher into the game. The coordinator might signal something like "Break right," "Blitz left," or simply "Hot!" When they do this, any player, even one who isn't normally a linebacker or defensive end, can leave their spot and rush the quarterback. Players can also cross the line during a handoff or on a sweep play if they are flowing to the outside. These are called "wide" crosses because they go beyond just the usual linemen. A back can cross the line too, even if it's illegal for him to do so. This allows the coach to have more flexibility with his offensive scheme and use different combinations of players on each play. Finally, a player can cross the line even if it's not legal for him to do so. For example, a player might cross the line to help block a defender off from the passer. Or he might cross the line to grab a receiver and pull him downfield.