According to Marquise Williams when they walked into practice Thursday this play was on the board as the first play against Duke. It was contingent on Duke lining up in the right formation and the Blue Devils did that. Williams explains the play here during his postgame press conference.
On the snap UNC has three receivers on the right with Ryan Switzer closest to the line, Mack Hollins in the middle and Quinshad Davis on the outside. Elijah Hood is the single back to Marquise Williams left. The Duke safeties are creeping up and look to be playing the run.
Williams hands off to Hood and Duke responds to it. Davis on the outside moves back taking himself out of the play, Hollins cuts to the outside for a downfield route. As Williams explained postgame, Switzer "slow plays the linebacker." He makes no real effort to get downfield so is largely ignored by the Duke defenders.
Hood comes up to the line, stops and pitches the ball back to Williams. At this point the entire Duke defense is committed to stop Hood's run. When Hood stops to make the pitch, Switzer hits the accelerator and takes off while Hollins continues his route at full speed.
As Williams winds up to throw the football he has not one but two options. Switzer is open down the middle of the field while Hollins is open on the outside with just Duke CB Breon Borders(#31) as the only player anywhere near the Tar Heel receivers. At this stage the only way this play doesn't result in a touchdown is if Williams makes a bad throw. He doesn't and Switzer scores with plenty of room to spare.
This was a gutsy call out of the gate by Larry Fedora and his staff. It clearly caught Duke off guard and essentially represented UNC popping the top off a can of you know what.
Here's the full play.