A Force-out Foul occurs when an airborne receiver catches the disc, and is fouled by a defensive player before landing, and the contact caused the receiver;
A Force-out Foul occurs when a receiver is in the process of establishing possession of the disc, and is fouled by a defensive player before establishing possession, and the contact caused the receiver:
Force-out fouls do not only apply to an airborne player. If, for example, a receiver catches a pass in the end zone, but before they are able to establish possession they are fouled, and the foul means they lose control, but they are able to establish possession in the central zone, that is a force-out foul and would result in a goal.