the basic running mechanics download has little gold nuggets that sink in the more you watch it. what stuck out most was the guy who was trying to lift his knees and his support leg would drop causing his hips to drop.
This is a common biomechanical flaw that I have observed in a spectrum of athletes competing in a spectrum of different sports. I believe it primarily to be an eventuality of coaching incompetence that permeates all spectrums. Whenever an athlete performs hurdle walk overs, any variety of power speed drill, or running activity they have the opportunity to do it with biomechanical efficiency or not (aside from rhythm, timing, fluidity, and so on).
I am in my second year of working with one of the most high performing (future Hall of Fame) players in the NFL and he has this very problem. He routinely drops the hips when performing any variety of sprint drills/power speed and initial acceleration. Last summer I had him perform a variety of drills to resolve this issue and we saw success (over a 5-6 week period);however, he has reverted back to his ways so we are currently working on it again.
I have found success with utilizing a few different drills which emphasize the complete extension of the support leg in both an alactic as well as lactic setting in which the elastic response is always present.