Quincy mentions the "constants". The old name was "absolutes".
I agree there are "constants" and they are difficult to pin down, but almost everyone who has swung in the mlb pattern has felt/recognized some.
What do you do to deal with how to define constants ?
Or do you give up ?
N&m$n , as an engineer, gave up. he said there was no such thing as absolutes. No such thing as "good mechanics". What you could learn the most from was an engineer able to understand a swing well enough to build a ground up model that would permit the understanding and consistency that would explain the swing with the same engineering principles that underlie the artificial model, then providing structure for how to approach learning the swing.
Unfortunately, building models involved OVERsimplifying the swing pattern to the point of not resembling how MLB hitters swing. N$man thought the simplest way was to adjust the torso up/down by bent at waist, then adjusting handpath in/out which was possible because if you hook/pull the handpath, you speed rotation up enough to get the inside pitch.
This is NOT how MLB hitters adjust for power hitting.This can be an option for 2 strike hitting or placement hitting or for other settings such as softball where hot bats are a factor.
So, if the N%man engineering approach is unsatisfactory, how DO you make the absolutes method work ?
I think there are 2 important approaches:
1- compare all authors describing MLB swing and "reconcile them". They are all describing the same pattern, so this is possible.
2-get perspective on the pattern from some other vantage point. The experience in golf provides this, the approach being best described by Jim Hardy in his PLANE TRUTH FOR GOLFERS series. More on golf:
In golf, where the ball on tee permits a much wider array of successful pattern/hybrids (which is a FAR more varied and complex situation than MLB), Hardy has figured this out.
There are 2 basic patterns that result in consistent/repeatable impact which are defined by how the arms connect to the torso. ALL golf info can then be sorted at a high level as belonging to one pattern or the other and the rest of the info that does not sort into one or the other is useless info.
Usually, the key info in each pattern is incompatible or the opposite of what is best for the other.
The 1 plane golf swing uses the shoulders to swing the arms around the body as the body turns. (PCR like)
The 1 plane swing tends to have a plane that is too flat/"shallow" and a path that is too wide. Remaining aspects of the pattern must work to make the swing trajectory steeper and more narrow.
The 2 plane golf swing swings the arms up and down as the body turns back and forth. (MLB like where it is OK to maximize swing plane steepness to the point of being "vertical" to match pitch, because you do not have to worry about squaring clubface in hitting).
The plane tends to be more steep and path/"sides of swing" too narrow in 2 plane golf.
Other pattern attributes must adjust the swing to be less steep and narrow if this is your preferred pattern.
ALMOST EVERY as aspect of the 2 golf patterns has an opposite requirement.
How you set up, where the weight is caried, how the hips move, sequence,etc,etc
Advice for one pattern is DEATH to the other.
For example, take the following golf "cues":
-Keep hands in front of body/chest.
This kills the 1 plane swing, but is sound advice for 2 plane
-Hit against a firm front side.
great for 2 plane, death to 1 plane.
-Stay down to ball.
great for 1 plane, death to 2 plane.
-Stay behind ball.
great for 2 plane, death to 1 plane.
ETC.
Now it turns out, the same 2 basic patterns exist in hitting, BUT only the 2 plane type pattern works in MLB which is why the cue "swing down" is still popular. MLB alos has to adjust spine/torso angle on fly (more influenced by shoulder tilt at top of torso, not bend at waist which is too proximal for adjusting on fly) as well as angle of connected lead arm ("weathervane").
Analytically, the ONE pattern that works in MLB is what Willams described as the "slight UPswing".
it is the equivalent of making everything a "low ball" type swing as oppose to swinging the bat around the body in the shoulder plane as you might think would be god for high ball.
These are 2 ENTIRELY different patterns, and, unfortunately, N$m&n, knowing nothing about hitting, chose to popularize the low level/"high ball" pattern that does not work, AND IS INCOMPATIBLE WITH, MLB hitting.
It isn't just that s-e-t-p-r-o (PCR/PCRW) info isn't perfect or has a different spin, it is that it has popularized on the internet with MANY followers, especially/moreso in softball (where it can be an improvement) a swing model and supporting info that will PREVENT learning the mlb pattern by training the body to move in an incompatible way, adjusting by bend at waist, brute force rotation, swinging bat actively with shoulders turning perpendicular to spine, just holding on to bat with hands, etc..
As DMAC noted, there is no way this can lift the low ball.
There is no way to adjust late. it is like swinging as if everything is a high ball you want contact by swinging the bat around the body with the shoulders, like making everything a tomahawk/swing down, NOT the slight upswing that Williams described (and many the other MLB authors such as Lau,LauJr,Peavy, Epstein, Slaught, Yeager, Mankin, etc.)
This "pattern based approach" has been figured out in golf AND it applies to the MLB swing.
IF you want to discover "constants" they should reside in these descriptions and in the descriptions of others describing this particular pattern, and should be reconcilable as compatible across numerous such descriptions.
There ARE absolutes, just as in golf. This is a good way to find them.
So is taking hacks yourself.
BUT, in MLB, the successful MLB pattern due to the requirement to adjust on fly is MUCH more homogeneous which makes this "reconciliation across multiple authorities" much easier than in golf.
You just have to figure out how to filter out the impostors like N%m&n.
If you are spreading the PCR?W info, you are an enabler, PREVENTING progress toward the mlb swing.