Former UFC Champ Matt Serra explains how to transition to the Armbar from the Back. A lot of people will go for the arm from the back but the transition is usually very loose and gives the opponent an opportunity to escape.
In the video Matt shares a couple of nice details that will keep the transition tight so that your opponent does not escape.
The first detail that I really liked was the way he trapped the opponent's arm that was defending against the RNC. The stiff arm that he used to control the opponent's posture was key.
Between this option and The Back Widow you should be snatchin' armbars left and right, literally!
