At my dojo and, I believe, ASU in general, we practice techniques from kata dori, which is a shoulder grab. Generally, you grab a handful of dogi right around the shoulder area.
1) Do you practice techniques from this type of attack at your dojo? A shoulder grab. Kata dori.
2) If so, do you also grab a handful of dogi?
3) Can anyone comment on where this attack comes from?
This is not common in koryu jujutsu as far as I can tell. What IS common in koryu jujutsu is eri dori, which is a lapel grab. But eri dori provides very different openings for a technique.
I am not a judoka but I have been told that a shoulder grab like this could happen while coming to grips. But it isn't a starting point. Maybe it is in some kata. Basically I am not satisfied that this is "a judo thing."
Not very common in Daito ryu, either....there is this aikirentai clip
...but this looks more like the standard judo grip, grabbing the sleeve around the bicep.
I don't like grabbing a handful of gi around the shoulder because I don't like mangling my fingers when they get all crunched up in the fabric. As often as possible, I simply grab the whole shoulder. I think having uke's palm open makes a better channel for entry and connection, but from uke's perspective it is a less effective attack, so it makes the technique less combative.