Can a player in the game be standing out of bounds then run over jump up and head a ball that is in the air but over the side line, with out stepping in before making contact with the ball.
USSF answer (August 11, 2009):
Assuming the ball had not left the field by crossing entirely over the touch line when the player headed the ball and that the player in question was not off the field with the permission or at the order of the referee, it doesn’t matter if that player at the time was partially or even entirely off the field. While players are expected to be on and to remain on the field during play, the Law allows a player to leave the field briefly if this is done “in the course of play.”
If the ball left the field of play before being headed by the player, then the continued play must be ignored because play is considered stopped whenever the ball leaves the field. If the player who headed the ball was off the field with the permission or at the order of the referee, then the player must be considered to have re-entered the field illegally (i. e., without permission) — play is stopped, the player is cautioned, and the match restarted with an indirect free kick for the opposing team where the ball was when play was stopped. These responses would be the case whether the player headed the ball or played it in any other way.