One of the most common errors that appears with kettlebellers of ALL levels is the squatting Swing. Instead of the kneecaps staying relatively fixed in space and the shins exhibiting minimal motion, some folks perform Swings with their shins swaying back & forth and their knees jutting forward over their toes. This happens when people "squat" into their Swings.
The Swing operates essentially on the same biomechanical platform as the Deadlift from the armpits down to the soles of your feet. That said, we need to revisit the 3 Prys and the Hard Style Lock again.
There are 2 main problems that need to be addressed with squatting Swings: lumbar strength & pelvic rhythm.
The lumbar spine needs the strength to maintain extension (a slight arch). Under load, the joints of the lumbar spine are in a biomechanically advantageous position if you keep them in extension. As soon as you fall into flexion, a couple of things happen.
1. The lower back is more vulnerable to injury because of the lesser degree of protection from the lumbar extensors.
2. The kettlebell drops out of the "upper triangle"* (formed by the knees and the groin), which tends to cause the lumbar spine to flex even further, the shoulders to elevate & protract, and the neck to "shorten". The arc/trajectory of the kettlebell becomes less of a Swing and more of a "scoop". If it sounds ugly or dangerous to you, that's because it is.
How your pelvis rocks back & forth is absolutely crucial when it comes to the ballistic lifts - Swing, Clean, & Snatch. The apex of each of those lifts should result in a solid Hard Style Lock. At the apex of the Hard Style Lock, the pelvis is posteriorly rotated slightly, thanks to the maximal contraction of the glutes.
--- BUT, the bottom of those lifts should look identical to the bottom of a good Deadlift, a la the 3 Prys. Thus, relative to the femurs, the pelvis is anteriorly rotated at the bottom. So the pelvis has to be MOBILE and COORDINATED enough to move with the direction of the load dependent on where it is.
The timing of the pelvic rhythm is actually pretty simple. If you maintain the Hard Style Lock as long as humanly possible while the bell is on the downswing such that the KB Swing trajectory stays well within the "upper triangle", you'll find that the hips "hinge" or "pry" backwards instead of squatting downwards.
Get back to your training, and train with intelligence and humility. The top dogs in the RKC organization aren't those who are clamoring to show off, but rather those who are jockeying to receive corrections from those who have taken their lifts and their understanding of those lifts to new heights!
As an RKC who came through to the recent workshop Kenneth Jay & I taught at Kettlebells Orange County said to her colleagues, "Things you know the Swing?.... THINK AGAIN!"
*More on the "upper triangle" another time.