Some people call it "turning the triangle" others call it "maintaining the box". I never actually understood the maintain the box analogy until at a Bustos clinic. She used a small square (I believe the base off some hitting tee) she used a girl to demonstrate. With the arms at 90 degrees she placed a corner of the square between the girls arms so when viewed from the side it looked like a diamond. Then when batter makes first move with lead elbow and slots the rear elbow she has them stop and holds the square base up again. Still fits perfectly between arms but now is a square instead of diamond, and she explained this was maintaining the box. I always did think it looked more like a triangle. Hope this explaination works along with bucketpapi.
Daddy O
We used a Schutt Travel tee and I held it against her elbows as she was leading with the knob of the bat inside the ball.
An engineer parent was quick to point out that even though the box/ travel tee is square it is a triangle in his opinion.
Thanks Howard