Artemis BJJ (Bristol Sports Centre), Can Sönmez, Bristol, UK - 14/01/2015
The americana is probably the simplest attack from mount you can do without a gi: the cross-collar choke is arguably as or more basic (in terms of the concept at least, the details can be complex), but that requires some kind of fabric to grip by the neck.
To begin the americana, grab their wrist with your opposite hand. Grasp their elbow with your other hand. Keeping both of your arms straight, lean diagonally forwards, using your weight to drive their arm to the ground (as per the picture, you can also follow Cindy Omatsu's example and use your head to add further leverage). The elbow of your wrist-gripping arm goes next to their head. Remove the grip you have on their elbow, then with your palm facing up, slip that hand underneath their elbow. As it slips under, turn your hand so the palm faces down.
With the hand you just slipped under, grab your other wrist. This means you now have a 'figure-four' on their arm, a solid grip. To complete the submission, keep your head down and lift their elbow, pushing their knuckles back in a straight line along the ground, like a paintbrush. You want to move their knuckles, rather than pulling their elbow down as well: that goes up (but only slightly), their knuckles go back. Also, keep the knuckles in contact with the mat.
You can also vary your angle, which will affect how far you have to push their knuckles. For example, Saulo Ribeiro teaches sucking the trapped arm in to their body, then lifting the elbow. His angle is such that he doesn't need to paint the hand back at all. It will also vary depending on the flexibility of your training partner's shoulder. Finally, you can try twisting your fists downwards, like you were revving a motorbike. That should further increase your leverage.
Teaching Notes: The angle of the arm can be tricky with the americana, something that will also vary depending on shoulder flexibility. Still, everyone got it eventually, especially as they'd all seen it at least briefly in the course of previous lessons. I tend to find it fairly tough to land from mount, at least in the standard way. Moving into higher mount and then applying it might be worth showing, though my option - really high mount and americana-ing against your own leg - requires you to already be comfortable moving up into high mount and maintaining the position. So, maybe not as useful for beginners? I could always give it a go.
I decided to throw in that other basic attack I mentioned before, the cross choke from mount. People were having some difficulty getting deep enough and also securing an effective twist. I had a go at showing it from guard instead, to see if that helped present the concept more effectively. It did seem to have some effect. It also highlighted that a big part of the problem was that they were finding it hard to get their hands in position in mount. In the guard, that's easier because you don't have to contend with the floor. It also meant I could suggest lifting their shoulders off the mat when attacking the choke in mount.