I've only done hack squats a few times and that was with a trainer and not a lot of weight. I have started to work the Wannabebig Routine #1, so I'm doing hack squats. This is my problem, on the way up the bar keeps getting hung up on my ham strings/ the backof my thighs and it can really throw me of balance. Also on the way down I keep hitting my calves which doesn't cause so much of a problem except the big red abrasion marks. I'm not sure what I'm doing wrong. This is how I learned to do them so you know what my form is:
Feet parallel, shoulder width apart, squat down with bb behind you right up on the ankles. Grip bb with palms facing back, butt out while arching your lower back and push straight up with your legs to full standing position always keeping your back arched. Reverse the process on the way down always arching your back.
Any help would be appreciatied.