re: Gordy Rush defensive film breakdown RE: losing contain

Maybe over aggressive but not really too small, at least to my view. I don't understand how, if a wide receiver moves towards the defensive end or linebacker to crack back block, the defensive back doesn't move up immediately to take over outside position. Could it be that the backs are actually following the receivers down the line too closely resulting in a bad angle once the back goes outside? I would think that this is something that can be easily corrected if that is the case.