We can't say this enough:
Every athlete is different, every hitter will use (or think they use) different triggers to get their body moving.
That's okay. There are 3 possible triggers for the start of lower body launch (after stride-load) and any one of them is acceptable to teach or use.
But here's the catch - you can't think, process, or sequence all 3. The brain can only be conscious of one action at a time; and if you tried to sequence them, the pitch would be in the catcher's mitt before you got the bat anywhere close.

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