Coach B’s instructions: when lifting the bar from the floor, keep a constant back angle while getting the knees out of the way. The whole purpose of the first part of the lift is to get to the ideal jumping position at mid-thigh, and if you change the back angle too soon you remove the opportunity for a powerful jump and successful lift.
With correct mechanics off the floor, you’ll reach mid-thigh in the right position for a re-bending of the knees during an aggressive jump that uses an “eccentric pattern” as you explode and drive the bar upward.
Video by Again Faster.
Additional reading: Supplemental Olympic Lifting for CrossFitters by Mike Burgener and Tony Budding, published Dec. 1, 2007.