Re: Jamming a technique
To me, jamming is the placement of an obstacle to prevent the execution of technique. I hear lots of judo players and MM artists talk about using their bodies to restrict their opponent's movement or restrict their opponent's ability to escape a technique, especially in dynamic movements. So it this sense of the definition, jamming is only a component of a tactic...what do you after you successfully jam your opponent? Jamming has its place as an entry into other dynamic movement (which I will not call kaishi waza...yet.)
I believe often aikido people [ab]use jamming because they do not know a logical conclusion to successfully jamming their partner. Once we stop our partner, we do not know what next to do so we end up hunkering down satisfied in our obstenance. Our stunned partner ends up with no energy; the kinetic energy was stopped and we are not providing any potential energy. The one-technique training style of aikido (kihon waza and sometime nagare waza) sometimes leaves newer students vulnerable to this type of exchange because they do not regularly train in a continuing format (henka waza) and are not able to spontaneously move into another technique.
In that measure, what are you learning by jamming your partner? Are you countering with a technique of your own? What is your partner learning? Is your partnering learning how to avoid being jammed? There is great training derived from these questions, but often not for beginning students who are trying to learn the basic movement mechanics. Nor for more advanced students to whom you cannot successfully jam on multiple occassions to create a consistent learning environment.
In short, jamming is not a problem as long as you and your partner have similar expectations and you can create a consistent learning environment to gain from the experience. Most of us in normal training cannot accomplish these elements and therefore we end up frustrated with the experience outcome (which neither meets our expectations nor can be reproduced for further evaluation).