The arm drag is a popular wrestling move and it has a lot of value in Brazilian Jiu Jitsu as well. It is a fairly simple move to learn, and it is easy to apply both standing and from the guard.
The arm drag involves getting wrist control with the same side arm, reaching across with the opposite arm and cupping the triceps (as close to the armpit as possible), then dragging and stepping around to take the back. It should be performed quickly, because if you are slow and sloppy it is easy for your opponent to counter.
If you are standing and have the back, there are a number of hug/backstep takedowns that you can do, and you can often just drag the opponent down, leaving you with a nice convenient position to get a rear naked choke or a bow and arrow choke. There’s a reason that the back is the most dominant position in a lot of people’s eyes.
The arm drag to the back can be done from closed guard as well. It uses a similar grip, and you drag the arm across your opponents body while hipping out to the opposite side. From there, reach up to grab your opponents lap, and pull yourself up to get the back. You can leave your trailing leg in place because it will simply become the “bottom hook” once the back take is completed. If you are doing sports jiu-jitsu, be sure to get those hooks in, because you need both hooks for back control to be considered points scoring position. For mixed martial arts or general self-defense, you might prefer the body triangle. It’s up to you what is more comfortable. Many people, especially those with long legs, find that a tight body triangle offers better control.
The arm drag is a very useful move to learn. It’s less risky in a lot of ways than shooting for a single or double, and it’s less hard on the body too. Shooting for a takedown on concrete isn’t fun, so for self-defense, you might find that either clinching up and tripping someone or using a body lock makes more sense. Even in sports BJJ, the arm drag puts you in a fairly good position since you take the person down and then get the back, giving you six points in total. Compare this to taking someone down and ending up in the guard (two points). From there, you could pass (another three points) or get swept (giving your opponent two points).
If you’re looking for something to drill as a beginner, then arm drags make a lot of sense. You can practice them by themselves or with a takedown, and you can even practice them on less knowledgeable friends since you don’t need to have the person you’re drilling with giving a specific response. This makes them an efficient and easy move to drill, so you can master it quickly.