Flipstop

Flipstop is a two-player game played on a square board of any size, initially empty. The top and bottom edges of the board are colored red; the left and right edges are colored blue. The two players, Red and Blue, take turns placing their own checkers onto unoccupied squares, one checker per turn, starting with Red. Passing is not allowed, but if you don't have an available placement, your turn is skipped. You win by forming a path of checkers of your color (interconnected via horizontal or vertical adjacencies, or both) connecting the two opposite board edges of your color. Crosscuts and captures A crosscut is a 2×2 area with two diagonally adjacent red checkers and two diagonally adjacent blue checkers. If your placement forms a crosscut, then for each enemy checker in the crosscut, if you can remove it and replace it with one of your own checkers without forming a new crosscut, do so. At the end of your turn, there must be no crosscuts on the board. Otherwise, your placement is illegal. Note: It isn't possible for a square to be an illegal placement for both players.