I used to have this same tight left hand problem a while back. The easiest way to fix this is to break the scales into 5 note increments. Experiment with how little hand pressure you actually need to make the note sound. You will be surprised that it doesn’t require much pressure at all. When you find the right L hand pressure, practice the 5 note part of the scale with just enough pressure on each note to get it to sound. practice it fast and make sure to keep the same amount of pressure. I think this will help a lot! It doesn’t matter if you hold your violin with your neck and chin or your left hand. I use my left hand.
Also, being still does inhibit your playing if you are used to bouncing around. If you practice whatever it is in small increments and make a point to not move, you will find (after it becomes comfortable) that it actually helps your playing. Then once you can play your piece well when you are still, then you might be able to play it even better when you move around. I was once in a masterclass with the famous violin teacher Robert Lipsett. He told me to stop bouncing around while I played and he held my scroll in place so I couldn’t move… It was very awkward.
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