I recently started training with my little brother who is 16 and the most athletic thing he's done so far in life involves his thumbs. That being said, I have him on starting strength and technically, he is progressing pretty quickly for only having lifted a total of 3 weeks. There is one main issue I have noticed while he squats though. Generally, he has solid form in terms of depth and setup. Still needs to tweak a few things here and there, but otherwise I've seen a lot worse. However, usually after a set or two, or if we add a few lbs to the bar, he starts doing this weird hula-hoop shit that leaves me baffled. I have seen it a few times on 'squat help' threads but I never really paid attention to the advice given since I never had this problem personally. I will try and take some video on my next lift day, Thursday, but does anyone have any idea what would be causing this? I don't think it's a spinal cord issue (e.g. scoliosis, I remember seeing that in a vid Urban posted if i remember correctly) and I would think it is probably a flexibility issue but he hits depth with ease. Thoughts?