If this question is what I think it is, the quarterback kicks his knee to signal a receiver or another backfield player that he wants them to start in motion, before the ball is snapped.
It is a signal to the wide receivers who cannot hear the snap count.
Dominick Jones, an obscure high school QB from a small town in Iowa.
In the NFL, yes. If the QB, or any player, drops to a knee purposely the play is whistled dead.
when the QB is not in the normal snap position and is back farther in the backfield.
intentional grounding
It means the next snap count by the QB will be the "real" one that will initiate the play.
Kurt warner
NO!
Douge flutie was the last person to have a drop kick field goal plus he was the qb too. Click on the 'NFL Dropkickers' link on this page to learn about some of the best dropkickers in NFL history.
Kyle Orton.
Reggie Ball
Vinny Testaverde.