The jerk support is a way to overload the overhead position for the jerk to build strength, stability and confidence.
 
Set up a barbell in a power rack at a height 2-3 inches below where it would be if overhead in a standing position with a jerk grip. Set your jerk grip on the bar and lower yourself into a partial squat under it with locked elbows. Make sure you’re balanced directly under the bar—some lifters like to hang off the bar to get centered and then place their feet on the floor.
 
With the trunk and upper back locked tightly, push with the legs straight up to lift the bar off the pins and hold steady for the prescribed time—usually 5-10 seconds. Lower the bar back onto the rack by bending at the knees.
 
Notes
The most difficult part of the exercise is usually the initial break of the bar off the rack and ensuring it’s balanced. Make sure you’re locking in the upper back and trunk tightly and squeeze the bar up off the pins rather than trying to lift it abruptly.
 
Purpose
The jerk support is a way to strengthen the overhead position for the jerk that allows the use of weights beyond what the lifter can jerk, or at least can or should jerk at that time. It can also help with confidence in the jerk.  
 
Programming
The jerk support should generally be placed at or near the end of a workout. Single lifts or 2-3 repetitions are most common. Weights can range anywhere from 90% to well over 100% of the lifter’s best jerk. Often a lifter can just work up to the heaviest possible on a given day.  
 
Variations
The jerk support can be done in the split position, or can be done as a jerk recovery—starting in the split and recovering to a standing position.