This play was in a recent JV game, Player A legally secured ball sitting on floor and lowered head and shoulders backwards to pass ball to a teammate who was behind him/her. That is a legal play. A very wise veteran official recently told me to imagine that the posterior of the player is the same as the feet when standing. If either "Cheek" is lifted it is the same as rolling to gain an advantage. Thoughts...Here is the Casebook Play.
4.44.5 SITUATION B: A1 dives for a loose ball and slides after gaining control. A1 is in a position either on his/her back or stomach. What can A1 do without violating? RULING: A1 may pass, shoot, start a dribble or request a time-out. Once A1 has the ball and is no longer sliding, he/she may not roll over. If flat on his/her back, A1 may sit up without violating. Any attempt to get to the feet is traveling unless A1 is dribbling. It is also traveling if A1 puts the ball on the floor, then rises and is first to touch the ball. (4-44-5b)