also: read option · the read
A zone run with one defender deliberately left unblocked. The quarterback reads him after the snap and either hands the ball to the back or keeps it.
The line runs a zone play and leaves one defender unblocked, most commonly the backside end on Inside Zone Read. The quarterback rides the back through the mesh while watching that defender. If he closes on the back, the quarterback pulls and runs through the space he left. If he stays wide for the quarterback, the ball is handed off.
Inside zone is the best-known version, not the definition of the play. Teams also attach the same give-or-keep decision to outside zone. What makes either one a zone read is the unblocked defender and the quarterback's post-snap choice.
read optionRPO, speed option, split zone and siftZone read and RPO are often used as though they were interchangeable. They are not: zone read chooses between two runs, while an RPO chooses between a run and a pass.