The Connect Four 7 trap is five of your discs in the shape of a 7: three in a row across, with a diagonal of three hanging down from one end. It's a strong shape because it makes two threats stacked in the same column, and your opponent can only block one of them. But it isn't the sure win it's often made out to be. In 1,120 games between two of our Medium computers, a player completed a 7 in 120 games and won 100 of them, and exact search showed the defender could have stopped it in 18 of those.
This guide shows what the shape looks like, why it works, when it fails and how to stop it. Every board was replayed by the engine behind Poozee's Four in a Row, and every number comes from seeded games between its computer players, checked with its exact solver. Red moves first in all the diagrams, rows are counted from the bottom and columns from the left. (Connect Four is a Hasbro trademark. Poozee's Four in a Row is our own version of the classic game, and we aren't affiliated with Hasbro.)
What the 7 trap looks like
The bar of the 7 is red's row 3 in columns 1 to 3. The stem is the diagonal from column 1, row 1 up to column 3, row 3, the bar's right end. That gives red two lines of three that both point at column 4:
- The bar needs column 4, row 3 to make four across.
- The diagonal needs column 4, row 4, the spot right above it, to make four diagonally.
The shape also works the other way round. In a mirrored 7, the diagonal hangs from the bar's left end and the two threats sit in the column to the bar's left:
We only count a 7 as a trap while both stacked spots are empty and on the board: a 7 whose bar ends at the edge, or whose bar is on the top row, has no column to stack its threats in. In the 1,120 Medium games we describe below, a 7 shape of some kind turned up in 304, but a live one, with both threats open, in only 120. Of those 120, 42 were mirrored.
Why two stacked threats can't both be blocked
A single threat can sit for most of a game, because nobody wants to fill the spot under it. Two threats directly on top of each other are different: they win as soon as anyone fills the spot under the lower one.
- If your opponent fills it, you drop on the lower threat and win.
- If you fill it yourself, your opponent has to block the lower threat, which opens the upper one, and you win there.
In the first diagram, the spot under red's threats (column 4, row 2) is already open. Red is threatening to play column 4 next turn, and column 4 again after yellow blocks. Yellow can't play there first either, since red would take row 3. Our exact solver confirms that every one of yellow's seven moves loses, and the same goes for the mirrored 7.
That's also why the 7 doesn't care about odd and even rows. In how to win Connect Four we explain why the first player wants threats on rows 1, 3 and 5 and the second player on rows 2, 4 and 6. That matters for a single threat, which only gets played when someone runs out of other moves. A stacked pair always has one odd and one even threat, and the builder can fill the column themselves, so the shape works for either player. In our games, most of red's 7s had the bar on row 3 (60 of 98 between two Medium computers), and when Hard played yellow it most often built them on row 4 (49 of 90).
How often the 7 trap actually wins
To see how the trap does in real games, we played one game from each of the 1,120 different positions after four discs, between copies of our computer players. Medium searches four discs ahead, never misses a one-move win or block, and breaks ties at random. Hard was held to eight discs of lookahead so every game replays exactly (in the game itself, Hard searches as deep as it can in 0.7 seconds). The first time each player completed a 7 with both stacked spots empty, we asked the exact solver who wins from there with perfect play. Each match names the first player first:
| Match | 7s finished | Builder won | Defender could stop it |
|---|---|---|---|
| Medium vs Medium | 120 | 100 | 18 |
| Hard vs Medium | 144 | 123 | 19 |
| Medium vs Hard | 134 | 102 | 32 |
| Hard vs Hard | 92 | 64 | 25 |
"Defender could stop it" counts the 7s after which the builder was no longer winning with perfect play. Only in 3 games, all Hard vs Medium, did both players finish one. A finished 7 turned up in 8% to 13% of the games, and it usually won, though not always on its own spots: between two Medium computers, only 35 of the builder's 100 wins ended with a disc on one of the 7's two stacked spots. But look at who built it. Hard's 7s against Medium won 202 of 219, while Medium's 7s against Hard won only 23 of 59. When both players were Hard, the builder lost 28 of 92.
The exact solver also explains why. In all 490 completed 7s across the four matches, the disc that finished the 7 never turned a draw or a loss into a win. Either the builder was already winning before it, or the 7 didn't save them, and in 16 cases completing the 7 actually threw away a win that a different move would have kept. By the time you finish a 7, the game is usually already decided: the 7 is how a winning position cashes in. Hard against Hard, the most careful pairing we tested, produced the fewest 7s of all.
When a finished 7 can still be stopped
A stacked pair loses its power when the defender has a threat of their own lower in the same column, or on the lower stacked spot itself. Then neither player wants to fill that column, and the old odd and even rule decides who has to.
Red's 7 looks finished, but yellow already has row 2 in columns 1 to 3 and the diagonal from column 1, row 1 to column 3, row 3. A red disc in column 4 would land on row 1 and let yellow win on row 2, so red can never start that column. Yellow's threats are on even rows, the second player's good rows, and the exact solver says yellow wins this position. Red's 7 never comes into play.
That was the pattern in almost every 7 that failed: across the four matches, 87 of the 94 7s that could be stopped had a defender threat in their column, on or under the lower stacked spot. Having one isn't enough by itself. Between two Medium computers, 42 of the 120 7s had such a threat and 17 of those could be stopped, while of the 78 with no such threat, just 1 could.
How to stop a 7 before it's built
The cheapest defense is to take the 7's last spot while it's still empty. Watch for four of the five discs with the fifth spot playable. Often the missing disc is the corner where the bar and the diagonal meet, as in this game.
Columns 3, 4 and 7 are full, so red has four choices. The exact solver says column 5, taking the star, holds the draw, and columns 1, 2 and 6 all lose.
We checked this across our Medium games. In 147 of them, there came a moment where one player could complete a 7 with their next disc and neither player could win at once. In 85 of those positions the defender was already lost, so the warning came too late. In the other 62, taking the 7's spot kept the best result the defender had in 59, and it was the only move that did in 33. When a 7 is one disc away, block it unless you can win first.
The 85 lost positions show the real lesson: by the time a 7 is almost finished, the game has usually been decided by an earlier slip. The best defense is the boring one, running the same checks before every move.
Pro tip: If you can't stop the 7, make a threat of your own in its column, below the stacked spots. If you went first, aim for an odd row there. If you went second, aim for an even row, like yellow in the diagram above.
Other traps worth knowing
The 7 is one way to make two threats at once, and there are others:
- The open three on the bottom row. Three in a row with both ends empty and playable wins on your next turn unless your opponent can win first, because they can block only one end. How to win Connect Four shows it, and how to stop it while it's still two in a row.
- Any stacked pair. Two threats on top of each other in one column win for the same reason the 7 does, and they're far more common than the 7 itself. In 688 of our 1,120 Medium games, a player made a stacked pair at some point, and the first one in the game came from a 7 in only 89 of them. The player who made it won 521 of the 688 games.
None of these beats a careful opponent on its own. Each one needs your opponent to have already let you aim two lines at the same spot or column, so look for them, but play every move with the three checks from how to win Connect Four: can I win, must I block, and what does the spot above my disc give away.
Practice the 7 trap
On Poozee's Four in a Row, Easy sometimes misses blocks, so it's the easiest place to build your first 7. Medium never misses a one-move threat, but it only looks four discs ahead, and in our games it lost 100 of the 120 games in which the other Medium finished a 7. Hard beat 36 of the 59 7s Medium built against it, and Hint shows the column Hard would pick for you. For the opening that sets all this up, see the best first move in Connect Four, and if you're the one defending, our guide to going second covers the even-row plan.
Keep playing
- Play Four in a Row and try to build a 7 against Easy or Medium
- How to win Connect Four: double threats and odd and even rows
- Best first move in Connect Four: every opening, from perfect play and our computers
- Going second in Connect Four: the best reply to the middle and the follow-up finish
- How to win tic-tac-toe, where every win is a double threat too
Frequently asked questions
Does the 7 trap always win in Connect Four?
No. It wins when the defender has no answer, which is often: in 1,120 games between two of our Medium computers, a player completed a 7 in 120 games and won 100 of them. But exact search showed the defender could still have stopped it in 18 of those games, and in all but one of them the defender had a threat of their own in the 7's column, on or under its lower spot.
How do you stop the 7 trap?
Take the spot that would complete it before your opponent does. When a 7 was one disc away and the defender wasn't already lost, taking that spot kept the best result in 59 of 62 positions we solved. Once a 7 is complete, your only hopes are a faster win of your own or a threat of yours lower in the same column.
Does the 7 trap work for the second player?
Yes. Its two threats sit on one odd row and one even row, so the shape works for either player. Between two Medium computers, the second player completed a 7 in 22 games and won 17 of them.
What is the best trap in Connect Four?
Any move that makes two threats at once: an open three on the bottom row, or two threats stacked on top of each other in one column. The 7 is one way to stack threats, but in our Medium games it made the first stacked pair in only 89 of the 688 games that had one.