The previous marker stays where he is and becomes the new receiver. With 4 people, people stay where they are. Good drill for marking technique and for pivoting on offense. With 3 people, allows thrower to work on a quick first step for a give n' go opportunities. One of the best drills for allowing instruction to developing players.
Markers invariably forget to call UP, or if they do, they say it too late or too softly.
Make sure people yell it out quickly. This is a good drill for marking technique. Offense is forced to pivot, otherwise D will camp out. This is a good drill for trying HRBs. Markers should practice marking close to the thrower's body.