Daniel Faggella is a BJJ Academy owner, Pan Am Champion, and writer for Jiu Jitsu Magazine, OTM, and more. If you want to learn more about grappling from the feet, download Dan's free Ken Primola interview and technique breakdown at: BJJeBooks.com/Ken-Takedown 
From the ground there are many options for attack, and you must always remain on the defensive in the case of one such attack. One may easily get their back taken, headlocks can be obtained, there are many options for a choke from here, or one might find themselves in the grip of a single leg. In this video, Ken shows us three important defenses from this position.
If we watch the video, we can see the importance of leaning the body back, using the same side body as the leg that is trapped. Apply pressure on your opponent; enough to make them uncomfortable and be forced to carry your weight. This instantly increases the level of difficulty they face in order to make their single leg offensive effective.
Next, you will want to grab your own ankle with the same side hand as the leg that is trapped, be sure to use the opposite hand to apply pressure on your opponent’s head; this is crucial. If the head is not receiving significant pressure, your opponent can easily turn this failed single led into a successful double leg. So remember, grab your own ankle, and apply pressure to both the head and the body of your opponent. From this position, you can easily step over your opponent’s head with your free leg and square up in a safe north/south position.
If your opponent has one hand trapping your knee and the other on the lower part of your leg, you will need to alter your defense accordingly. Lean back in a similar fashion to the previous defense.
Next, you will want to lean your trapped leg towards the same side it is trapped on. For example, in the video Ken’s right leg is trapped. When he leans it away, he leans towards the right. Remember, just like the previous defense, pressure on the head is crucial. This will crush the hand of your opponent, thus loosening his grip on your leg. From here you can easily slide back into a north/south position.
This defense is effective if your opponent is attempting to isolate your leg from behind you. His head will be on the outside and he will have one hand trapping your knee and the other holding your ankle. From here, you will want to use your same side arm as the leg that is trapped and use it to reach under the armpit of your opponent. Once your arm is inside, grab your opponent’s forearm and simply pry it up, thus releasing your leg.
You could also opt for the second defensive method Ken demonstrates. Again, apply pressure to the head. Next, swing your free leg around, up and over your opponent, placing you perfectly in a north/south position and freeing your opposing leg in the process. This technique seems simple enough and looks impressive when done while rolling.
These are just a sampling of the many techniques that can be used from these positions, not to mention the submissions they could easily be turned into. It's all a matter of reacting to what your opponent throws at you. The more tools you have to react with, the more effective you will be at rolling. So, take what you have learned here, practice it and play with it; see what else you can come up with. Maybe you will find yourself combining two or three of these techniques together. Remember, its position over submission, as long as you get into a better position, you've done well. Take what you have learned here and keep rolling!
Daniel Faggella is a BJJ Academy owner, Pan Am Champion, and writer for Jiu Jitsu Magazine, OTM, and more. If you want to learn more about grappling from the feet, download Dan's free Ken Primola interview and technique breakdown at: BJJeBooks.com/Ken-Takedown