[FMadera]

A player may touch the floor across the center line with one or both feet/hands provided a part of the foot/feet or hand(s) remains on or above the center line. Contacting the floor across the center line with any other part of the body is illegal.

Basically, as G87 indicated, in NCAA, you can cross beyond the center line with any part of the body provided there is no safety hazard and there is a part of the body on or above the center line.

In NFHS, anything other than the hand or foot beyond the center line is illegal, period. If it's a hand or foot beyond the center line, part of it has to be on or above the line.