Take turns marking individual squares. The first move of the game can occur anywhere; after that, you must play on the mini-board dictated by your opponent’s previous move. How so? Whichever square they picked, you must play on the corresponding mini-board.

If you place three in a row on a mini-board, then you win that miniboard. The board is now closed; any player sent there may move anywhere they like, on any other board.

Three mini-boards in a row wins the game.