This signal is used by the Referee to indicate that an illegal use of hands or illegal block in the back foul has occurred. When against the offense it is usually for a block in the back, but covers a multitude of sins by the defense.
PenaltyThis is a 10 yard penalty and it will be assessed from the basic spot.
If it is called against the defense on a forward pass play when a defender fouls an eligible receiver - this attracts both a 10 yard penalty and an automatic First Down.
Begin with one hand held close to and in front of the chest with the palm facing forwards and the other hand grasping its wrist. Push gently forward by about a foot.
Finally point to the offending team by streching an arm out from the shoulder to the horizontal.