"Will Smith"

I'll bite.  Honestly, I see a lot of (controlled) movement in his hands and legs that works for him.  He must have exceptional timing and balance with all those moving parts.  I don't think I'd try to teach somebody how to hit like this.  This is a huge swing by a smaller guy (5'10" 195) so I understand he is trying to generate transfer power from his lower half and backside.   I've never been a fan of the big leg kick.  However, if you have the talent to do it and produce some positive numbers then why change it.  They've got him hitting 4th in the lineup so there is a pretty good reason for that.   That big leg kick can leave him more susceptible to breaking and off speed pitches.  I'm not a fan to giving pitchers more of an advantage than they already have.   In looking at Will Smith's numbers, he does strike out quite a bit at approx 20% of the time over the last few years.

I much prefer the swings of Ohtani and Kyle Tucker as they have simple swings.  I like simple.  https://www.youtube.com/watch?v=IpgHBzYrVL8

JMO.

Fenway;

Notice the bat angle. He holds the bat straight up & down, as it is lighter in his hands and avoids the 3/4 angle which can produce a " longer swing path".

Yes, the "leg kick" is his timer and can "counter-productive with talented professional pitchers.

Watch his eyes, as they are "riveted" to the pitchers release point.

Bob

What I saw was a swing that is really quick and a bat path that is short to the ball. Hands are inside the ball, the angle of attack is really good, and he gets great extension after contact. Not to mention the barrel being in the hitting zone a long time. His fundamentals are very solid.

Reminds me of Buster Posey.

https://www.youtube.com/watch?v=2CKyxbUdbgw

Novice round:  I see some big ass strong muscles, literally in his gluts and hams.  And he's very balanced for as much movement as seems to be going on, not really moving forward until his hips are rotated.  Explosive bat speed too (I might have cheated on that one).

I like the swing a lot. Yes, there is some movement but it is synced very well. If you do knee lift, hand pump you have to do it exactly like him, I.e knee to front elbow and then separate as the knee moves back down again.

I would not teach that to a kid with limited body coordination but for a guy like Smith who has a little fringy (by mlb all star standard of course not by general hitter standard) batspeed but great plate discipline so that move can help him to get a little extra stretch in the load.

Obviously if you have a guy who has the batspeed but already some plate discipline issues you likely don't teach that move but if you have a well coordinated and advanced hitter with great plate discipline I'm not against doing some experimentation with that kind of load.