Kick the ball into the enemy goal — White scores in e8, Black in e1. The ball starts on e4. There are no pawns and nothing can ever be captured except the ball itself; other pieces only block, like defenders marking players.
Kicking: move one of your pieces onto the ball's square to capture it — the piece takes possession right there. But it can't hold it (nobody could ever steal the ball back): immediately click a dot or drag the ball to launch it. It rolls away like that piece moves, from the square of the capture: a rook smashes it down the file, a bishop bends it along diagonals, a knight chips it over defenders. Rolling balls stop at the first piece in line.
Passing: if the ball lands on a teammate, they immediately must launch it again — as often as you like, all in the same turn. The turn ends only when the ball comes to rest on an empty square. Enemy pieces block the ball and can never be landed on; the goal squares always count.
Turns: kicking is never forced — capture the ball when it suits you, or just move a piece.
Threefold repetition, stalemate or 200 turns end in a draw. No checks — kings are just players.