WOW! My first ever post on this thread. I can't believe it. I better make this a good one.
OK, someone needs to delve more into the extension of the pelvis because I know how much it helped me to learn about this aspect of the golf swing. Thanks to @james_hirshfield for teaching me this very important piece.
So we all know about the lateral move the hips have to make on the downswing aka the slide (or "bump" if you're a Hogan disciple). And obviously we have our rotary component, but everyone knows that one. All well and good. But, the third major component that can often be overlooked is understanding that the pelvis goes from 1) flexed forward at address to 2) varying levels of extension on the backswing to 3) back to flexed forward in the early downswing to 4) extending through the strike and finally 5) fully extended at the golfer's finish.
Many good instructors refer to this piece as "tucking the butt."
Check out the two ends of this spectrum. @Mulligan Jeff on the left, Gorilla James on the right (a long drive guy):
Hopefully the difference in the hips/pelvis of these two golfers is clear as day. Gorilla James hits like 300 yards 2-irons BTW.
Here's a video Mark Crossfield did that talks about this stuff:
Here's @james_hirshfield talking about this as well. This vid is for those of you who love to know exactly what's happening biomechanically:
Pelvic thrust or tucking the butt is a major component in allowing the hips to continue to rotate. This is also massively important to getting one's weight forward.
People who do this incorrectly do it towards the golf ball, so a major key in learning this is doing it along your tush line, so keep that in mind here.
Here's an old @Beachcomber swing from 2012. He's TST's resident "goat humper" (slang for someone who extends the pelvis incorrectly), which he's done a lot to fix over the past couple years, so kudos to him, but I'm using this old swing as an example of how people can get this wrong:
You can see how his butt comes off "the wall" or red line here. Beach still played to a 3.0 so obviously this very much so tends to be a better player's mistake. Still, his swing exaggerates this piece so much, it's a good one to look at to learn the general basic motion -- the only difference is you should do this along your "tush line," not out towards the ball, or in this case, to his right.
From face-on, we can clearly see how much he's doing this, so again, it's a great swing to learn this piece from:
Again, the red line represents where his hips were at address and the top of his backswing.
Watch Zach Johnson do this while keeping his "butt on the wall:"
From face-on this should be clear as well. The pelvis is not staying in its flexed forward position. Often times, you'll actually see high handicappers increase the amount their pelvis is flexed forward through impact and to their finish.
Zach certainly does not do that:
As you can imagine, extending the pelvis to allow the hips to continue rotating AND getting one's weight forward is obviously super critical to overall downswing sequencing. It's a piece that is completely absent in high handicap golfers by and large.
So if you've seen your swing on video and you think this information applies to you, try it out.
I hope this post was helpful in some way to someone out there.
PS- There's a reason people refer to it sometimes as "goat humping," the key word here being "humping." Yes, they're joking when they use that term, but "hump" is pretty darn descriptive over what's happening here. Think about that one for a sec, so I don't have to get too graphic here. But this is something every guy should know how to do instinctually