I've gotten some questions on 'over-acceleration' of the clubhead. It's actually a term from 'The Golfing Machine' which author Homer Kelley warns the reader against. I believe that 'Over-Acceleration' and 'Quitting' are almost synonymous with each other, so I'll explain 'Quitting' first. 'Quitting' is a slowing down or stoppage of the hands thru the impact zone.
Let's take a look at the swing sequence of the antithesis of 'flipping', Mr. Lee Trevino.
Take a look at Trevino's hands in frames 7, 8, and 9. At frame 7 the hands are by the right thigh. Then in frame 8 they are in between the legs. Then in frame 9 (impact) they are by the left thigh.
It's safe to say that Trevino's hands are moving 'forward', more towards the target right through the impact zone and they are moving at a pretty steady rate.
The golfer who 'quits' basically comes into the impact zone and their hands stop moving towards the target like Trevino's do in the swing sequence above. Or if they don't exactly 'stop' they slow down a whole bunch. Thus the term 'quitting.' Here's about the best pic I could find.
Look at this golfer's hand LOCATION at impact. At impact, his hands are about opposite of his right leg. That is about the same LOCATION as Trevino's hands in frame #7. Except Trevino's clubhead is nowhere near making contact with the ball and instead the clubshaft is about parallel to the ground.
So what happens with the flipper is that his hands go from the top of the swing to about his right thigh on the downswing. And then once they about reach a point by the right thigh, they either slow down or stop completely. BUT, the force of the swing means that the clubhead will reach the ball and make contact somehow. So, if the hands are not moving and DRIVING, the only way that clubhead can come in contact with the ball is to bend the left wrist and flip the wrist thru the ball.
Now, one of the reasons why golfers 'quit' is that they actually over-accelerate the clubhead. Over-acceleration is something that usually happens right in the impact zone and consists of the clubhead going past the hands. However, a lot of the time it happens in the start down. The golfer gets too fast on the start down and by the time they reach impact, the clubhead has now over-accelerated past the hands.
There's other causes for this as well. A poor pivot is one of them. If the pivot is poor or stalling in the impact zone, it's very difficult for the golfer to keep driving those hands thru. That's why when we chip or pitch, we usually do it from a slightly open stance. The chip and pitch swing is so short that we really don't have much time to pivot, so by opening the stance up we more or less 'pre-pivot' and thus the hands can keep driving thru impact.
However, that's also why using 'basic' and 'acquired' motions are so effective in learning the proper impact alignments. In these motions you really shouldn't open up the stance (aka 'pre-pivot') and thus you need to force yourself to pivot just enough and keep those hands driving thru impact.
I also think a problem with a LOT of golfers is that it starts with the right index finger and the right thumb. Ben Hogan referred to the right index finger and right thumb as 'swing wreckers' and I find this to be incredibly true with a ton of golfers. If you were to take a clubhead and 'flip' thru impact the easiest way to do so is to do it with the right index finger and right thumb. This also flattens out the right wrist.
To delve even further, the pressure of the flip caused by the right index finger seems to get in the middle joint of the right index finger. This is interesting because many golfers use the #3 Pressure Point which is the base joint of the right index finger, and 'aim' it at a point out in front of the golf ball. So IMO, having pressure less than an inch away can be the difference between a flip or a flat left wrist.
However, I think golfers should probably think about the other pressure points besides the #3 PP. The 'swinger' can use the #2 or #4 pressure point and the 'hitter' can use the #1 PP (which is what I use). But, if you were to drive the hands steadily forward, you find that the only way you can do it is with some sort of pressure. That's why I have been talking about lag not being about 'maintaining ANGLES' it's about 'maintaining PRESSURE.' If you have pressure you can continue to drive those hands forwards, sustain the lag and have that flat left wrist at impact. If you lose the pressure, then all of that is for not. As Homer Kelley said, lag is ELUSIVE, meaning once you lose it...it's gone. Once you lose that pressure, it's gone and not coming back. That's why my swing feel is primarily to bring the maximum amount of pressure at impact. If I get it at the startdown, I'll lose it pretty quickly and come impact it's already gone. LAG IS ELUSIVE.
And I hate to harp on this, but another reason why the Taly is such a powerful training aid. It teaches the golfer how to keep those hands driving forward and eradicating 'quitting' and eliminating 'over-acceleration of the clubhead.'