Chapman demonstrating beautifully a portion many throwers that are on the brink have trouble with: maximizing their weight shift.
You’ll note that Chapman starts off with a fairly slow tempo, but BEFORE peak leg lift he flips a switch. We see a posterior pelvic tuck (disengages quads), and he’s able to transfer his lateral energy rotationally into footplant.
The part I feel is most often missed? Disengaging the quads. Without that aspect in place, we’ll see a vertical move into footplant vs the rotational move Chapman is able to achieve here. Once you “sit”, don’t stand back up. Let the lower half rotate out from underneath you.