Re: Principles of pinning
I'd like to call attention to some jujitsu pins used by the British army introduced by one of their COs from the world war era. Of pins, they are not exactly standard types, but used for practically immobilizing a prisoner whilst allowing the soldier to remain mobile and dangerous.
One of which I recall implicitly was to have the prisoner climb rope like on a pole or a small tree then have him sit straight down without releasing his leg grip. This pin is excruciating and prevents anyone, absolutely anyone from standing up or releasing themselves. Prolonged periods of enduring this will of course result in permanent disability, which back in those days were the least of their problems I guess.
For the modern world we live in, I guess attacking centerline would be as basic as you could get in terms of principle.
As for those touch/awase type pins... Like I said, obtuse people will get put of it because they'll run away. Most aikido with good ukemi though won't get out of it because they need to ensure the safety if their necks even as they try to escape. Which to me is kind of weird in a way. Since being pin means it's the end of story anyway.