Learn how to do a basic arm bar used in BJJ. Alex Schoenauer and Steve Cantwell, both Sergio Penha Jiu Jitsu black belts and seasoned MMA fighters, take you through the basics.
Start with control by grabbing your opponents Gi, from the lapel or wrist. If you have the wrist by the Gi, you take your other hand and grab the Gi behind the outside of their elbow. Put your foot on their hip, trapping their arm and then shift your hips while pushing off their hip. Now kick up your other leg higher under the opposite arm you are controlling.
Next, throw the same side leg over the top of the arm you have to the back of their neck and apply pressure.
As Alex points out, there are some finer points that prevent you to posture up and once you stretch their arm out, you leave your opponent no other choice then to start tapping.
It is two against one, meaning two of your arms working, controlling one of your opponent’s arms.