Offense always has an advantage over defense in pretty much any team sport, because defense is most often on the reactive side of the football. The play action pass takes advantage of the slight delay caused by reaction times to help downfield receivers get into an open position to make a catch.

The play action pass is actually very simple. A play action is a fake handoff by the quarterback to a backfield player, either a halfback or fullback. The purpose of this fake handoff is to cause the linebackers on the defensive side of the line to hesitate, since it is their job to stop any running play that overcomes the defensive line.

But it is also the linebacker's job to provide additional coverage for short range and medium range passes, especially in zone defenses, where linebackers must control several yards of the field immediately behind the defensive line.

By faking a handoff, the quarterback causes the linebackers to hesitate so they cannot drop back into pass defense quickly enough to prevent a successful reception.