Is this an IP?

[DTQ_Blue]

PONY rules. Pitcher engages plate w/both feet and brings hands together. Then lifts pivot foot about 4 inches completely off plate while hands are still together and left foot is still on plate. Pivot foot then comes back down, and as soon as pivot foot is back on the plate, she separates hands and delivers the pitch.

If this breaking of contact of pivot foot with plate illegal? If so, I'd also like to know why.

Thanks,
Mike