Squats form- bar slipping backwards?

[Subsistence]

Today squatting I had a really hard time with the bar slipping backwards. I seemed to be leaning forward to counter this. I couldn't even get the bar up as high as I am supposed to when putting it back on the hooks. I had no problems on my last session, so I am shocked that 5lbs would do this, I feel I must somehow have really screwed up my form. After the 5x5, lower back and left part of my ass was tight/ aching too. It went away after a few sets of overhead press, but still obviously wasn't good.

Any idea on what I am suddenly doing so wrong?

[holvoetn]

Make sure your chest is up as much as possible.
If this happens again, maybe you can post a video so we can check.
Or if there is someone in your gym who knows how to squat, ask that person to check while you squat.

[chris88]

Your not placing the bar the right way on your back. I had the same problem when I started stronglifts. Try to look for some sort of shelve on your shoulder blades. Also watch out that your back is as tight as possible and that your chest is up.

[l1n3n01z]

Elbows back!

[Wellhairedbeast]

Also make sure that the back of your wrist runs with your forearm in a straight line and is pushing the bar against your back. Also make sure you make you make your back really tight prior to gripping and unracking the weight, otherwise you wont be as tight and secure.

[oggynosh]

Also make sure that the back of your wrist runs with your forearm in a straight line and is pushing the bar against your back. Also make sure you make you make your back really tight prior to gripping and unracking the weight, otherwise you wont be as tight and secure.

Exactly...I've noticed that if I dont tighten my back before unracking the bar I have a hard time squatting :s.... ...so do as all my fellow lifters have told u dude...