This is a fundamental movement that I rarely seen taught. It does take a good understanding of body mechanics and , if used properly, timing.
I start off by showing a very static version for students to fit into the position, and then I demonstrate the movement how I was taught. Ultimately, I think both of these versions are sub par, but they do remove the most difficult aspect of this move...the timing.
Once the student understands how the mechanics work, it is important to add in the timing. The 3rd demonstration of this move puts a timing aspect. It is very important to work with your partner and them roll with the movement. Be very careful when applying this movement live, if they are not prepared for this move, you should let up on your training partners and dont punish their ignorance with a broken arm.
In competition, they are responsible for their own arm, and this move works very well.
I end the video with a Triangle from side control body. This was something that worked well as a blue belt, occasionally as a purple, and then never again. It's a crap move, but it is important to know that it exists.