Re: The shoulder grab - where does this come from
More of an explanation but also how itīs trained at a more advanced level. In basic practice itīs common to just grab and hold (as in katate dori etc). Kata dori is also useful as a training method since itīs easier to understand to use the body instead of just the arms to drive the waza (ie simpler than in katate dori).
Any static grab is a pretty silly form of attack.