Continuing a takedown after opponent has sprawled (ie opponent of top of you):
1) Put both your hands on the back of there legs, don't grip, just hold.
2) Drive forward, holding the legs
3) Move your head to one side and out to whichever side is underhooked (otherwise the head is trapped)
4) Continue to push forward and twist sidways into their body (use head as lever) to take them down
Taking the back after opponent has sprawled (ie opponent of top of you):