Trapping the elbow as our opponent shoots for the underhook. They go for the position under the arm to try and set up a variety of throws, or gain positional control. What we have lying in wait for them, is a potential shoulder lock if we can get it. If they dive the arm deep to save it, then we follow up with tight arm control and a solid frame as we strike with knees, and/or go for takedowns.
The following are a couple of takedowns I like to use from this position - White Ape Falls In Hole, and Monkey Goes Over Falls.