Explanation:

There are two rows of participants, facing each other.

A. Even number of participants:
The person in the left lower position remains there throughout the sequence; the rest rotates as indicated.

B. Odd number of participants:
There is no person in the left lower position; the rest still rotates as indicated. The person in the left upper position sits out.

After one full rotation everyone has sparred with everyone else (including the ghost in case B).

P.G.