p.boxed
  | Pieces turn around the board, they cannot go in the middle.

p.
  Each side has only a king, two rooks, one bishop and two pawns.
  Pieces can never enter the central area.
  Pawns can only move "clockwise", acording to the image below: they move
  and capture forward straight and diagonally in the arrow direction.

figure
  img.img-center(src="/variants/Rollerball/rollerball_directions.gif")
  figcaption.text-center.
    Main directions on the board.
    The squares where direction changes are enlighted with white arrows.

p.
  When a pawn reaches the starting square of an enemy pawn, it promotes
  into a bishop or rook.

p.
  Rooks and bishop move as usual, but are restricted to one square only when
  moving counter-clockwise.
  Moreover, they are allowed one rebound in certain circumstances:
ul
  li a bishop rebounds on the first wall met,
  li a rook rebounds (at 90 degrees) if it reaches a corner.

figure
  img.img-center(src="/variants/Rollerball/rook_example.gif")
  figcaption.text-center Some rook movements.

p.
  The king moves as in orthodox chess.
  The goal is either to bring your king on the initial square of the
  opponent's king, or to checkmate him.

h3 More information

p
  | See the 
  a(href="http://history.chess.free.fr/rollerball.htm") author's presentation
  | , and the 
  a(href="https://www.chessvariants.com/40.dir/rollerball/index.html")
    | chessvariants page
  | .

p Inventor: Jean-Louis Cazaux (1998)