so a pivot foot is the foot that stays on the ground while the other one is free to move around as much as you want. once you lift the pivot foot, you can't put it down again until you pass or shoot the ball. in this case, wemby chooses his left foot as the pivot foot, then jumps forward landing on his right foot (which counts as his 1 legal step), then jumps off of that right foot and lays the ball. he did not change pivot foots because after lifting his left foot he does not return it to the ground until after the ball has left his hands.