Joe Brockoff, 19 year coach at Tulane, and former Yankee minor leaguer says:
Ever hear of squish the bug in baseball? This phrase refers to the pivot of the back foot as the batter swings the bat. In this case, the back foot "spins" on the ball of the foot, like we do when we squish a bug.
Here is what the result will be:
Some people believe that it is important that hitters be on the ball of their feet at the Point Of Contact. This is variously known and taught as "squishing the bug", "squish the bug", "squashing the bug", and "squash the bug". Proponents of this idea includes some people who instruct at the major league level.
Unfortunately, this isn't what the best hitters do.
What does an MLB Player's Back Leg Look Like at Contact?
Sammy Sosa HR #599
Do not teach Squish the Bug
Squishing the bug is a bad cue most often used to make a hitter finish their hip turn.
The cue usually results in a fake hip turn that actually prevents a hitter from fully turning their hip.
MLB players don't Squish the Bug. The action of the back leg is a result, not something that can be cued.
So, fix the real problem instead.
Correcting incomplete hip turn
If your hips are not turning, then your back elbow is not slotting into your hip,
and you are not maintaining the slot and the 90 degree elbow until you are facing the pitcher.
Squishing the bug in order to assist in hip turn usually results in turning the back leg instead of actually turning the hips, or finishing the hip turn.
I call this a fake hip turn.
Squishing may actually hinder a complete hip turn.