Keep the trail foot down to constrain pelvis rotation
Asked why he keeps the left foot on the ground, he says he does not mind a little lift but keeps it down as a deliberate limitation. Lifting the foot too much gives him too much pelvis rotation and too much movement; keeping it on the ground constrains the pelvis and sets his range. He does not think lifting the foot adds any acceleration or speed.
Channel: Todd Graves
Watch official source at 31:52