One of those techniques is called "throwing hot," which entails intentionally leaving one blitzing defensive player unblocked. The offensive line usually makes pre-snap adjustments so that the "free" rusher is clearly within the QB's field of vision. This limits devastating blind-side hits on the QB by rushers. When the preparedness of a quarterback allows him to not have to worry about getting hit from behind, it is one less psychological element of the blitz to be taken away, and thus blitz is incrementally made less effective by that particular element.