It's either a ball out of bounds, or an illegal participation by an out of bounds player. He's not inbounds until he lands in bounds.

A ball thrown out of bounds may touch or be touched by players in the OOB area without penalty. However, if any of those OOB players deliberately touch the ball before it crosses the side line, it should be flagged as illegal participation.

An OOB player can also be guilty of illegal participation if he deliberately touches players on the field during a play.