Getting "trapped" and swing plane
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It is tough to tell without video, but he may be referring to your right elbow getting stuck at your side because you are taking the club back too low. Check out this thread.
I had this issue with taking the club back too flat and not keeping my elbows closer together. My right elbow would get stuck at my side and my swing was coming over the top a bit.
I was at the range yesterday morning and a gentleman approached me and gave me his card-he is an instructor. It was a slow morning and he had been watching me swing from a distance. He told me my posture and swing were generally good, but I was causing myself to get "trapped" and the top. He wanted my to "go up" in stead of around more at the point in my backswing where the club shaft became parallel with my toe/shoulder line (my hips, toes, and shoulders were square at set up). in other words, keep the shaft in parallel with my toe line. I tried to do as he said, and did make better contact. So did this mean I was getting "laid off" and "stuck"at the top? Is this correction good advice? I am thinking of taking a lesson or two from this gentleman.