From Chewjitsu:
In this video I show a sneaky arm lock from the back mount when someone defends a collar choke.
In many cases a basic concept that I stick with is that if you attack the neck, the arms open up. If you attack the arms, the neck opens up. So you can switch back and forth between the two to open up submission options from the back mount.
This technique and the setup is an example of that.
Start by attacking the collar choke from back mount. Once the person defends, which they will have to, you will often have the option of snagging an arm.
The sneaky part of the arm lock comes from the fact that we are going to bait the person into escaping. It’s definitely a gamble, but if you drill the technique you’ll feel that you actually have a fair mount of control from the position.
I actually used this technique in the finals of an IBJJF tournament and then used it in the Pans that same year with success.
It’s deceptive and a lot of times people don’t see it coming.
So give it a try. I’ll add that you will need a rudimentary understanding of how back mount works and some basic controls from the position. Assuming that you do though, go ahead and try to work this when you’re training.