The S Mount is so much more than a transition to an armbar. The S Mount is a way to punish your opponents for allowing you to get to mount in the first place. No one does it all better than James Clingerman.
In this video, we see how to get into the S Mount position and how to make it as painful as possible for our opponents. Clingerman teaches us to use the Americana to set it up, and how to get the armbar finish. Give it a watch, and be sure to add this gem to your game.