Thanks. I'm just not comprehending, some imbecility is blocking me. I believe I'm doing that (keeping shoulder closed). I apply speed by torso rotation after a solid plant and shift, and I'm doing better at keeping arm relatively loose. But when I apply speed, the elbow kind of pulls the hand along a narrower plane (closer to my body) before the hand finally speeds up and whips out. So I get decent hand speed, but a crappy arc.
I've noticed from your other videos (and videos of other competent throwers) that when you actually throw a disc, there's a pronounced K shape, where I can see the disc change back to wide from narrow, much more than the hammer is doing in your posture video. I see that the whole throw needs to be smooth, no jerky pauses or stops, but unless I specifically pause and "throw" my hand/lower arm out (basically bouncing it away from my chest/pec right after it gets there), I don't get that arc change (or rather, I get it too late).
And maybe that's what I need to do, keep working that pause and bounce until it becomes smoother and faster. I had shoulder surgery a few years ago (tenotomy; they cut the upper bicep tendon) and I wonder if maybe that affects this a bit too. I probably need to film. I'm probably not as closed as I think I am. But if I try to exaggerate a really late, ultra-closed feeling, I put a lot of stress on my plant knee and it's not at all smooth or athletic.
Anyway, thanks so much for your insight and advice. I'll try not to pester, but I just did some field work yesterday so it's all fresh in my mind.