Curing the "Butt Wink" in the Squat
Here's a great video from Juggernaut Training Systems discussing the dreaded "butt wink" in the squat. There are a lot of differing opinions about whether this pelvic movement is dangerous, and Dr Quinn does a good job of breaking the movement down.
Squatting of all forms will typically involve some degree of pelvic movement and this will shift the neutral spine within a relatively safe range. The key is good core activation and core control while having awareness of proper squat stance and movement.
Take a peek, worth a watch.