Also - you don't see it much but watch old clips of Stan Musial swinging - his back foot left the ground all the time - seemed to work out OK for him.
it you look at video most good hitters the back foot does leave the ground.
If by leaving the ground you mean when the batter starts running I agree.
The videos I saw of Stan Musial and Ted Williams had their foot on the ground at contact.
i assume you want to argue over .01 seconds or there about, search pictures and video of swings, most MLB, along with college, good HS and good youth swings have the hitters back foot laces pointed to the pitch, toe to the ground on the very tip of the toe moving forward a few inches either dragging or slightly up in the air...there is an endless stream of them if you care to look.
at the end of the day hitters have .4 second to hit from release to the plate, at least .1 of that is needed for reaction...the entire swing takes .3 or less - and we are going to argue if the tip of the toe is still down or not at contact...seems silly. one thing i thinkg we can all agree on is if you are not turned and rotating forward and you haven't transitioned your weight to the frontside with tilt...you are late!! if we can't agree on that there doesn't seem much to discuss.
