How to use Brazilian Jiu Jitsu to Defend Against Punches on the Ground
Many people became involved with Brazilian Jiu Jitsu because of the powerful, proven system of self defense techniques created over the last century. In the wide world of sport BJJ competitions, it's easy to forget just how incredibly effective jiu jitsu is from a wide variety of ranges. Nowhere does the self defense application stand out more than when you're on your back, defending against someone trying to punch you. Here is a fundamental strategy for dealing with an aggressive opponent who is attempting to punch you. With their fists, even.
Control the Range
The first thing to consider when you have someone in your guard trying to hit you is the distance. Generally speaking, when you're defending yourself, you either want to be very far away (read as: outside of punching range), or very, very close. The general concept here is to close the distance quickly, and preferably only once, as your partner throws that first big punch. Once they've given you the momentum you need to break their posture down, the concept is to keep them down and minimize your risk of injury due to punches and headbutts. Finally, once you have them in the range where you want them, the overarching goal needs to be not to let them go!
Overhooks and Head Redirection
Assuming your partner is punching you with their left hand, the general concept here is to swim for inside control with your right arm, creating a shield out of your arm. As your partner is throwing this punch, pull your knees in close to your chest, bringing your partner forward much faster than they originally anticipated. While you still have this inside control with your right arm, push their head over to the side, redirecting any potential inadvertent (or intentional) headbutts. Be careful when doing this in practice, as the headbutt is about as likely as the punch to land! From here, you have an overhook of sorts with your right arm, snaking around your partner's arm (either all the way, as with a traditional overhook, or just by pinching your armpit over your partner's arm). Now it's difficult for your partner to posture back up to hit you. Finally, if they try to hit you with their right arm, you can step on their hip, using your shin as a shield (and you can also set up a very nice overhook triangle from here).
Another possibility from inside your closed guard is that your partner may look to amplify their punches by posting up on one foot. Assuming it's with their left foot, you can enter straight away into a scissor sweep here by turning onto your side, driving your right shin across your partner's waist, and continuing to control their head and arm. Because your partner's weight is back and then rushing forward, the momentum for the sweep is a sure thing. Keep in mind that you'll need to react fairly quickly here, so drilling and making the movement automatic is important.
Finally, your partner may also elect to grab your throat in order to pin you down and then slam down a punch with much greater accuracy (and force). When your partner grabs your throat with their right hand, just pivot so that you are perpendicular, and then throw your legs up into an armbar position. A nice bonus: this technique works just fine in sport BJJ as well.
Punch Defense: Tougher on the feet, or in the guard?
While there is a great deal more material to cover regarding blocking punches in BJJ, the good news is that the gross motor skills involved with the fundamental movements shown here are very simple, and once done a few dozen times, become virtually automatic. These are the building blocks for a more nuanced self defense game, but the same skills and motions are frequently used in sport jiu jitsu (think about the ubiquitous inside control, or overhooks, or controlling distance). All of these things combine together to make it very easy to "practice" these techniques, even when you're not technically setting out to practice them. Repetition is the key to improvement over time, and you'll get repetitions from rolling. As always, let me know if this tutorial helps you understand this topic!