In gomoku the attacker holds the initiative: each of their moves forces yours. The defender who only reacts will eventually meet a double threat they cannot answer. The defender who reacts and builds at the same time will eventually find the attacker out of forcing moves, and then the roles reverse. This article is about that second kind of defence.
The idea: every block is also a stone
A blocking stone does not disappear after it stops a line. It stays on the board and belongs to four lines of its own. If you choose blocks that line up with each other, your defence slowly becomes a structure. By the time the attacker runs out of threats, you may already have twos and threes waiting.
The practical question on every defensive move is: among the points that stop the threat, which one touches the most of my own stones?
Choosing between equal blocks
Many threats offer two or three blocking points: the two ends of a three, or the gap and the ends of a split three. They often stop the threat equally well. The difference is in what they do for you.
For each candidate, look along the four lines through it:
- Count your stones within four points on each line.
- Note whether those lines are open or already blocked by the opponent.
- Prefer the candidate that creates a two or three on an open line.
A block that makes you an open three is especially strong: now the attacker must answer you, and the initiative has changed hands in a single move.
When to stop defending
The attacker's forcing chain ends when they play a move that does not threaten anything immediately. At that moment you have a free move. Most defenders waste it by blocking a harmless two. Use it instead to make your own strongest threat.
Rank your options:
- A four that also blocks something of theirs.
- A four-three or three-three of your own.
- An open three, especially one that crosses their lines.
- A quiet move at the opponent's landing point (where they could make a double threat).
Option 4 is defensive, but it is still better than blocking a random two, because it removes their best future attack.
Counter-fours when under attack
When the attacker creates a threat you cannot answer, such as a four-three, a counter-attack with fours is the last resort. A four must be answered, so every four you play buys time. If one of the opponent's forced blocks lands in a harmless place, and your chain of fours ends with a four-three of your own, you win first.
You can only use this if you have prepared fours in advance. That is the real reason to build while defending: it stores up counter-fours for the moment you need them.
The blocked ends rule gives defenders extra tools
Under the Vietnamese blocked ends rule, a five needs at least one open end. A defensive stone placed at one end of an enemy line has lasting value: that line can now win only toward its other end. Place a second stone at the far end later and the whole line is dead.
This creates a counter-attacking style unique to caro: defenders who close enemy lines on both ends while building their own. In freestyle, closed fours can still win, so the style works less well.
A worked habit
After each forced block, spend a few seconds on these questions:
- Is the opponent still threatening something, or did my block end their chain?
- If it ended, what is my strongest forcing move?
- If it did not, which of my candidate blocks builds the most?
It sounds like a lot, but most of the time the answers are obvious once you look.
An example of the switch
Picture a typical middle game. The attacker has made an open three on a horizontal line, and you block it at one end. They respond with a closed four on a diagonal, and you block that too. Then they play a stone that connects two of their twos, but creates no immediate threat. This is the moment.
Look at your two blocking stones. They sit two points apart on a vertical line, with one of your older stones just below them. Filling the point between them gives you three in a column, open at both ends. The attacker must now spend a move on your three, and while they do, you look for a second line through one of those stones. Two moves ago you were defending; now you are the one making threats.
This does not happen by luck. It happens because both of your blocks were chosen with the vertical line in mind. Had you blocked at the other ends, the same free move would have produced nothing.
Mistakes that kill counterattacks
- Blocking far from the centre. Stones on the edge touch fewer lines and rarely become part of a counter.
- Answering a quiet move with a quiet move. When the attacker pauses, you must act, not tidy up.
- Playing a three when the opponent has a three. Your three does not force anything if they can make an open four first. Only fours override their threats.
- Forgetting the opponent's landing points. A counterattack that ignores their next double threat usually loses a move later.
Patience is part of the counterattack
Switching to attack too early is as costly as never switching at all. If you make a three while the attacker still has a forcing chain, they simply ignore it, play a four, and your three is wasted. Wait until the attacker's chain has genuinely ended.
Practise
Against the computer on the home page, choose the third level and play Black (O), which means you start one move behind. Try to win by counterattacking. Every time you win, look at the moment the initiative changed hands. Further reading: block early or late and surviving a four-three.
Frequently asked questions
How can a defender win in gomoku?
By blocking in ways that build their own lines, then attacking when the opponent runs out of forcing moves.
Which blocking point should I choose?
The one that stops the threat and touches the most of your own stones on open lines.
What should I do with a free move after defending?
Make your strongest threat, ideally a four or a double threat. If you have none, take the opponent's best landing point.
What is a counter-four?
A four you play while under attack. It forces the opponent to answer and can break their attack if their forced block lands badly.
Is counterattacking easier under the blocked ends rule?
Somewhat. Lines you have closed at one end stay weak, so your early blocks keep paying off.
