The first thing that comes to my mind when I hear brazilian jiu-jitsu is ground fighting which is the beauty of this martial art.
Giving a person the necessary set of skills to be able to defend himself in a street fight situation and granting him the ability to fight from an inferior position ( off his back) is the core of brazilian jiu-jitsu.
Most of the bjj practitioners, especially the bigger guys, consider being on your back a bad position to begin with even in a sport environment, for example a competition. As for the white, being put on your back and getting your guard passes on a daily basis can be very frustrating and demoralizing.
One of the reasons for this is that developing a crafty and offensive guard usually takes more time and effort than, for example, passing but this doesn’t mean that the guard is not a dangerous and effective position in bjj but also it provides with a wide spectrum of submissions and sweeps. One of the most common and basic submissions you can use off your back is the armbar.
Altho most people, even at the higher ranks rely on speed and deception while setting up and finishing the armbar, the proper technique is the key to a successfully done armbar. One of the most important details in the armbar is hip movement and angling. Getting the right angle of the armbar is crucial, because it makes it that much harder to escape or defend it, but also it sets you up in a more natural positions for your hips to move and your joints to bend in order to finish the submission.
Another key detail is positioning your opponent’s arm, which is a very common mistake among beginner belt levels. Most of the white and blue belts just flip the leg over the face and crank on the arm, but this sometimes works and sometimes doesnt , depending on the previous setup. The thing that will make the armbar that much tighter is pulling and positioning your opponent’s arm on your body while you move your hips. The arm needs to be atleast on the center of your stomach or at the best case scenario, to be pulled to the opposite shoulder of where your opponent is.
This greatly reduces the window of escape for your opponent and it makes it neatly impossible to defend at this point. Just to mention, controlling your opponent’s posture is very, very important because of he regains his posture that means that nothing of the above wont work. Breaking the posture down is one of the most important things that needs to be done while going for submissions from the closed guard, not just the armbar but lots of others aswell.