I had never heard that myself so I googled it and found this
Nelson hold - Wikipedia the free encyclopedia on Wikipedia, where towards the bottom, in talking about the Full Nelson, it says the following:
"The full nelson (sometimes called a double nelson or a double shoulder lock) is done by performing half nelsons with both arms.
In collegiate, high school, middle school/junior high school, and most other forms of amateur wrestling, the move is illegal. The holder is on the back side of the opponent, and has his or her hands extended upwards under the opponents armpits, holding the neck with a palm-to-palm grip or with interlaced fingers. By cranking the hands forward, pressure can be applied to the neck of the opponent. The usage of the full nelson in
combat sports is very limited. It is a secure hold which can be used to control the opponent, but does not allow for finishing action, such as
pinning the opponent, executing a reliable
submission hold, or allowing for effective
striking.
[2] Because it can be used as a limited
neck crank, it is considered dangerous in some grappling arts, and is banned, for instance, in amateur wrestling."
I bolded the pertinent portion.
As I said, I had never heard that. I seem to recall seeing it applied in the professional wrestling I used to watch on TV when I was a kid. I know in the Hapkido I learned, we had effective defenses against the full nelson.