#15 is a coach standing on the sidelines
Everyone sprints
Sprint more.
Sprint again...
Halfway back, the coach throws the disc to a random location on the field and designates one of the teams as "offense," the other team is on D. (Red will be on O, for this example.)
Now it's an endzone drill, but since the players didn't know who was O and who was D until a second ago, they need to quickly set up their plan and avoid transitional mistakes.