Head Movement In The Jerk
How can you push the bar back off your shoulders in the jerk if your chin is in the way?
Easy! Get your big dumb head out of the way!
This can be done by pulling your head straight back or tilting it back—most often a combination of both is best.
How exactly this is done and looks will vary among lifters depending primarily on build. A lifter with a massive chest and tiny head won’t have to do as much as a lifter built like Olive Oyl with Bruce Campbell’s chin.
It can help to imagine thrusting the chest up through the bar as you finish the drive and push off with the arms—this both helps keep the rack position strong and extends the upper back, which brings the head back out of the way more.
In any case, we want to try to maintain the same forward focal point throughout the motion for balance and orientation, which means not throwing the head back excessively.
Finally, I recommend starting the jerk with your head already partially pulled back—don’t try to go from totally neutral to all the way back in the time it takes the bar to move an inch off your shoulders. This can be done with the combination of that big chest posture and pulling and tilting the head back partially as you set the rack position.