Zhanlue is a simultaneous-play version of Connect-Four.
In simultaneous-play games, both players enter their move, with neither able to know what the other is about to play.
If both players select the same column, then the move is forfeit, and each player must select another column to play in. If all columns are used up in a continuous series of forfeit moves, then the bottom row of the board is discarded and the whole board shifts down by one. If this shift causes a repeated position then the game itself is forfeit and each player gets their bet back.