Boarder and Nogi are clinched. Boarder begins to "pummel" his right arm in (he brings his right arm in to underhook Nogi).

Boarder is half-way through the "pummel". As he gets his arm in...

Boarder quickly does a level-change, bending low with his knees, as he sidesteps to the side of Nogi.

Here's another angle of the step above. As Boarder is doing the level-change / sidestep, he lowers both his arms down so that they grab behind Nogi's thighs. Boarder's head is also tight against the hip of Nogi.

Here's yet another angle shot of the step above. Boarder's leg should be positioned behind Nogi's leg.

And yet another angle. One thing to remember is that Boarder goes around when he sidesteps, as pointed out by the green arrow. He doesn't go in straight. Boarder should be more to the side than this pic suggests.

Boarder drives through, using his weight, legs, and arms to push Nogi down. Boarder will go on his right knee as Nogi goes down.

... and Nogi goes down. I couldn't take a pic of them as they fall, so I placed a weight on Boarder's legs and used an envelope to hide the weight.

An alternative to the usual double-leg is for Boarder to wrap his right leg around Nogi's leg as he takes him down. It's not that clear in this photo, but that's he does.

Note: Boarder doesn't push Nogi straight backward, he pushes him back and to the side at an angle, as pointed out by the green arrow. This makes it easier to take Nogi down and I think it makes it harder for Nogi to get guard.

As soon as Nogi is down, Boarder transitions over to establish side control.

Boarders gets side control and underhooks both arms.

Boarder applies a lot of shoulder pressure, making Nogi uncomfortable. Boarder posts on his head. He is preparing to get mount.

Boarder slides his knee across Nogi's belly as he gets mount.

Boarder gets mount.

Boarder maintains both underhooks. Here, he controls both arms by squeezing his elbows in and holding the top of Nogi's head.

Same step, different angle of above pic.

Boarder brings his left knee up high.

Maintaining control of both arms (more the the photo shows), Boarder shifts his position and moves his right leg.

Boarder transitions to the armbar. Boarder can optionally post with his right hand on the mat or on Nogi's hip to help with the transition. Also, Boarder should be holding both of Nogi's arms tight (the Snowboard Instructors wouldn't let me squeeze the arms).

Boarder finishes the transition and finishes the armbar.

If Nogi manages to free one of his arms, no problem. Boarder still has the other and can still complete an armbar.