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If you’re going to give the old squat stance a go, make sure you’re not getting any pain symptoms (not only during the session, but in the night and day following).
Also, be careful of how you interpret the pictures in BaSL. Both Kelly and Diane have exceptional hip and ankle mobility, and are able to achieve some extreme of range of motion at the bottom of a squat that allow them to stay very upright. It’s not about pushing your knees outside the feet, but rather pushing them outwards to create tension (as Rippetoe himself said in Starting Strength). Your knees may, however, track outside of your feet when your hip and ankle ROM reach that level and you’re training a more upright squat. This is, to some degree, a result of the knee tracking farther forward in these deep upright positions creating the visual effect of the knees being waaaaaaay out.
A good rule of thumb is that your feet should always be fully planted on the floor. If you push your knees out too far (trying to look like the Leopard), your feet will peel up and you’ll end up squatting on the edge of your foot, which is a fault. I find it helpful to pair the knees-out cue with “screw your feet into the floor” and “big toe down” to help emphasize that connection.