Some starter athletes misunderstand the meaning of "squat like you are sitting on a chair or a toilet". Hence they tend to keep their hips more than out during squatting leading to lower back injury.
Johnnie Walker - Keep Walking
"Move me out of the away so that someone else can lift": Ed Coan after injuring himself during a squat attempt of 970 lbs in 2002
POWERLIFTING - ABSOLUTE POWER