Re: Principles of pinning
Most common to rare...
Pain and mechanical leverage.
Dynamic intent (to continue attack on uke's chushin)
Passive reshaping of uke's atari.
Absolute harmonization with uke's energy.
The first two is probably the most understood method and the easiest to be overcome. Depending on uke's determination and complete obstinance to the fact that nage can attack him at will in any pinning position, which basically translates well to police work. Uke here generally disregards the officers ability to trash him during a pin because of potential law suits.
The 2nd two are ideal methods that does not force uke into anything and in fact puts him against himself. Some other arts do get very similar here... I'm thinking certain Silat can lock up even multiple opponents without dynamic intervention... But thenthey don't explain the secret very well.