This is a common formation used in football which allows the offense to either run or pass the ball. The pro set is popular because of its flexibility and is used at all levels, including the National Football League.
This formation consists of five offensive linemen and a tight end on the line of scrimmage, a wide receiver flanked on either side of them, and two running backs split behind the quarterback. The formation is flexible because the offense can either hand the ball off to one of the running backs or pass the ball to one of the wide receivers. Because of this flexibility, the defense is left guessing both what type of play is coming and its direction.
In addition to confusing the defense in regards to play type and direction, the offense can also use the pro set to fake one or the other. Since either a pass or run could be the desired execution, faking a run and passing the ball, also known as, "play-action," keeps the defensive line and safety pinned to the running back while the quarterback and wide-receivers work to pass the ball. Another advantage for the offense is the extra protection the running backs can provide to the quarterback on a passing play.