Four in a Row looks simple: seven columns, six rows, and gravity. Line up four discs of your colour across, up or diagonally. Underneath, it is a game of threats stacked above each other, where the row a threat sits on matters as much as the threat itself.
Rules
The grid has seven columns and six rows. Dark moves first. On your turn you drop one disc into a column that is not full, and it falls to the lowest empty space in that column.
The first player to get four of their discs in an unbroken line, horizontally, vertically or diagonally, wins at once. If all 42 spaces are filled without such a line, the game is a draw.
There is nothing else: no captures, no passing. Every column you fill changes which spaces can be reached next, and that is where the depth of the game comes from.
Strategy
Claim the centre column. It takes part in more possible lines of four than any other column, and whoever settles there first gains real influence.
Make two threats at once. A single threat is easy to block. Look for a disc that creates two places where your fourth disc would win: the opponent can only fill one of them.
Mind the rows of your threats. A threat you cannot use yet, with empty spaces below it, still shapes the game. As a rule of thumb, the first player wants threats on odd rows counted from the bottom, the second player on even rows.
Never play under a threat. If the opponent wins on a space, do not fill the space directly below it: you would let them drop the winning disc on top. Late in the game, the side that runs out of safe columns loses.
Questions
Can the first player always win?
On the standard 7×6 grid the first player can force a win with perfect play starting in the centre. The computer is not perfect from the first move, but at Master it plays the last part of the game exactly.
What counts as a line?
Four discs of the same colour next to each other in a row, a column or either diagonal. More than four in a line also wins.
Is a full grid a draw?
Yes. If all 42 spaces are filled and nobody has four in a line, the game is drawn.
Why did the computer not block my threat?
On the lower levels it sometimes misses things on purpose. From Strong upwards it blocks immediate wins and avoids filling the space under your threat.
How do I play on a phone?
Tap anywhere in a column; the disc drops into the lowest free space. With a mouse, hovering shows where the disc will land.