The play is set up when the disc is in the middle of the field. The reset handler is set up on the break side so that the defense can't poach off the reset
The back of the stack sets up their cut and cuts under.
As the back of the stack cuts under the front of the stack cuts deep. This is supposed to make the defender guarding the back of the stack choose to play help defense or protect the under
In this case the defender guards the under and leaves the deep space open allowing for a big huck