JKD & BJJ Position really is everything

Case in point King Leonidas and 300 of his spartans fought and held against the vastly outnumbering legions of Xerxes. In the context of fight sports positioning makes the unmovable sweepable, the untouchable strikable, and the undefeatable beatable. This especially true in the half-guard position. Originally the half-guard was the result of your opponent attempting to pass your guard. This was a place you ended up in, not one you fought from. However as sport jiu-jitsu has evolved the half-guard has evolved as a offensive position of its own, notably by such jiu-jitsu players such as Roberto "Gordo" Correa and Eddie Bravo (see "Jiu-jitsu Unleashed" (Eddie Bravo)).
In BJJ we worked three sweeps from the half-guard. The primary key to playing the half-guard is to remain oblique to the mat, that is, up on one side (shoulder and hip) never flat on your back. Also the hooking leg (bottom side) should drop the toes to the mat as a better hook.

1. Half-guard ankle pick

   Using your top-side knee and forearm, frame at the hip and neck. Pummel the frame inside to an underhook as you simultaneously extend the the top leg, dive your head to their far knee. This flattens your opponent, allowing them to fall into the "black hole" caused by the removal of the frame and the repositioning of your body. Reach your bottom side hand through and catch the far foot from underneath, slide your underhook arm down and pass the trapped foot to this hand. Bring your bottom elbow in to your body and then slide it to post, transition out and unhook your leg, then redrive into your opponent rolling them to the mat. Incidently you can pass the guard in a very similar fashion of passing and trapping the foot.

2. Taking the back

   You attempt the half-guard ankle pick described above, but your opponent sprawls out. Reverse your position and use the underhook to shuck forward and attack the back with a Marcelo Garcia "seat belt" grip. Climb to the back and secure hooks.

3. Whizzer counter sweep

   In this scenario your opponent blocks the above attempt at taking the back by putting in a whizzer, essentially overhooking your underhook. They want to drive your forward with this pressure, you will defend by posting out, creating a strong frame. Now pinch your upper arm down on the whizzer, punch their knee with your posting hand, and dive your head to their far knee. If they have strong (realistic) forward pressure they will literally roll them selves forward into th spot where you used to be.

This can be easily drilled by switching between the taking the back and the whizzer counter sweep while having the top player switch between defending with whizzer and posting against the sweep.
During the JKD portion of practice we worked on advancing and retreating while using the downward and upward figure 8 patterns. Talk about positioning, a mistake earns you a crack on the hand or noggin'.