The ball weave is great for the core. This exercise looks flashy, but in reality, your abs are in a static position the whole time. There is very little movement in the midsection. The ball weave is easy perform, but it does require some coordination.
Start in the supine position (on your back). Slowly bring one knee toward your chest. As you do so, weave a small ball through the leg and retrieve the ball with the opposite hand. Alternate the ball weave between both legs. When done correctly, the legs should move in a bicycle fashion. The key is to contract the abs at all times. Your abs must remain in the "crunch" position for this exercise to work. The shoulder blades should come no higher than a few inches off the floor. Be sure to keep the head straight and chin up. Do not crank the neck.
Lie on your back with ball.
Contract abs and weave ball between legs.